JP2006282161A - Run-flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a run-flat tire increased in run flat travelling distance, while restricting an increase in the weight thereof. <P>SOLUTION: The run-flat tire 1 is provided with a carcass 6, a belt layer 7 arranged outside the carcass 6 in the radial direction of the tire and arranged inside a tread part 2, and a side reinforcing rubber layer 9 arranged in a side wall part 3 and having a substantially crescent cross section. In the side wall part 3, a side reinforcing code layer 11 formed of at least one code ply 11A is arranged. The side reinforcing code layer 11 is extended along a main body part 6a between a radial directional outer end 11o of the carcass 6 pinched by the main body part 6a and the belt layer 7 and a radially inner end 11i of the tire positioned in the vicinity of a bead core 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a run flat tire that can continue running even during puncture.

  For example, a run flat tire is known in which a side reinforcing rubber layer is provided with a side-reinforced rubber layer having a substantially crescent-shaped cross section having a high load supporting ability (see Patent Document 1 below). The run-flat tire suppresses the amount of bending of the sidewall portion even at the time of puncture, and can run continuously, for example, about 100 km.

  However, even in a run-flat tire, as the travel distance in the puncture state increases, the sidewall portion gradually generates heat due to periodic bending deformation, and as a result, thermal destruction occurs in the internal rubber material and cord material. If the run-flat tire is run further continuously, the sidewall portion generates heat up to about 200 ° C., completely loses the load support capability and falls into a running impossible state. Therefore, in order to increase the run-flat travel distance, it is important to reduce the deflection of the sidewall portion and suppress heat generation.

  In the conventional run flat tire, a large side reinforcing rubber layer is used in order to suppress bending of the sidewall portion. However, such tires are heavy and deteriorate fuel efficiency. Moreover, since the rubber thickness of the sidewall portion is increased, the heat dissipation is likely to deteriorate. Therefore, the current situation is that a sufficient improvement effect is not obtained.

JP 2002-301914 A

  The present invention has been devised in view of the above circumstances, and a side reinforcing cord layer having cords is arranged on the sidewall portion, and the positions of the outer end and inner end in the tire radial direction are appropriately set. The main object is to provide a run-flat tire that can increase the run-flat mileage while minimizing the increase in tire weight.

  According to the first aspect of the present invention, a toroid-shaped main body extending from the tread portion through the sidewall portion to the bead core of the bead portion, and the main body portion connected to the main body portion and around the bead core from the inner side in the tire axial direction to the outer side. A carcass including at least one layer of folded ply made of a cord having a folded portion folded back, a belt layer disposed on the outer side in the tire radial direction of the carcass and inward of the tread portion, and disposed on the sidewall portion. A run-flat tire having a side reinforcing rubber layer having a substantially crescent-shaped cross section, wherein a side reinforcing cord layer comprising at least one cord ply is arranged on the sidewall portion, and the side reinforcing cord layer is , An outer end in the tire radial direction sandwiched between the body portion of the folded ply and the belt layer, and the body portion and the folded portion Characterized in that between the between and radially inner end which is positioned in the vicinity of the bead core extending along said body portion.

  The invention according to claim 2 is the run-flat tire according to claim 1, wherein an overlap length of the side reinforcing cord layer and the belt layer in the tire axial direction is 5 to 40 mm.

  In the invention according to claim 3, a bead apex extending in a tire radial direction outside from the outer surface of the bead core is disposed between the body portion and the folded portion of the folded ply in the bead portion, The side reinforcing cord layer extends between the bead apex and the main body, and an overlap length in the tire radial direction between the bead apex and the side reinforcing cord layer is 5 to 40 mm. Run flat tire.

  The invention according to claim 4 is the run-flat tire according to any one of claims 1 to 3, wherein the side reinforcing cord layer includes the same cord as the folded ply.

  The invention according to claim 5 is the run flat tire according to any one of claims 1 to 3, wherein the side reinforcing cord layer includes a cord having a modulus larger than that of the folded ply and a high heat resistance.

  In the run flat tire of the present invention, a side reinforcing cord layer having a cord is disposed on the sidewall portion. The side reinforcing cord layer includes an outer end in the tire radial direction sandwiched between the main body portion of the carcass folded ply and the belt layer, and an inner end in the tire radial direction positioned between the main body portion and the folded portion and in the vicinity of the bead core. Extending along the main body. Such a side reinforcement cord layer can reinforce the sidewall portion and increase the run-flat mileage while minimizing an increase in tire weight. Further, since the side reinforcing cord layer does not excessively increase the thickness of the side wall portion, it is possible to prevent the heat dissipation of the side wall portion from being deteriorated.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a right half sectional view of a run flat tire 1 of the present embodiment. The run-flat tire 1 is disposed on the toroidal carcass 6 that extends from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and on the outside of the carcass 6 in the tire radial direction and on the inner side of the tread portion 2. Further, a belt layer 7 and a side reinforcing rubber layer 9 having a substantially crescent-shaped cross section disposed on the sidewall portion 3 are provided. In this embodiment, one for a passenger car is shown.

  As the passenger car tire, a tire having a low flatness, for example, a tire having a flatness of 20 to 65% is preferable. Such a tire having a low flatness ratio is particularly suitable for a run-flat tire because the side wall portion 3 has a small height and the side portion has high rigidity. The tire 1 is provided with an inner liner rubber 15 made of rubber that does not easily transmit air on the inner surface of the tire 1, and the internal pressure can be maintained by the rubber 15 when the tire 1 is not punctured.

  In the present embodiment, the carcass 6 is formed from a single folded ply 6A. The folded ply 6A is formed by covering carcass cords arranged in parallel with a topping rubber. For the carcass cord, organic fibers such as nylon, polyester, rayon and aromatic polyamide are suitable. In this example, polyester is used. Further, the carcass cord is inclined at 75 to 90 degrees with respect to the tire equator C, for example.

  The folded ply 6A includes a toroid-shaped main body portion 6a extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and both ends of the main body portion 6a and around the bead core 5 in the tire axial direction. And a folded portion 6b folded back from the inside to the outside. In this example, there is a high turnup structure (HTU) in which the outer end 6be of the folded portion 6b is located on the outer side in the tire radial direction with respect to the flange height of the regular rim J, more specifically on the outer side in the tire radial direction with respect to the tire maximum width position M. Indicated. Such a high turn-up structure can effectively reinforce the sidewall portion 3 with a small number of plies. Further, in order to reduce the weight of the tire, a low turn nap structure (LTU) in which the outer end 6be of the folded portion 6b is positioned radially inward from the outer end of the flange of the regular rim J may be employed. The carcass 6 can also be configured using a plurality of folded plies.

  Further, a bead apex 10 is disposed between the main body portion 6a and the folded portion 6b of the folded ply 6A. It is desirable that the bead apex 10 is tapered from the outer surface of the bead core 5 to the outer side in the tire radial direction, and is formed of, for example, a hard rubber having a JISA hardness of 65 to 95 degrees, more preferably about 70 to 95 degrees. This helps to increase the bending rigidity of the bead portion 4 and suppress the vertical deflection of the tire 1.

  The height ha of the bead apex 10 from the bead base line BL is not particularly limited. However, if the bead apex 10 is too small, the durability during run-flat running tends to decrease. There is a risk of deteriorating ride comfort. From such a viewpoint, the height ha of the bead apex 10 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 belt plies 7A and 7B on the inner and outer sides in the tire radial direction in which a belt cord made of steel is inclined with respect to the tire equator C at, for example, about 10 to 35 °. The belt plies 7A and 7B are overlapped so that the belt cords cross each other, and the carcass 6 is tightly tightened to increase the rigidity of the tread portion 2. Since the inner belt ply 7A is wider than the outer belt ply 7B, the outer end 7e of the belt layer 7 is defined. The belt cord may be made of a highly elastic organic fiber material such as aramid or rayon, if necessary, in addition to the steel material.

  In the present embodiment, a band layer 8 is disposed outside the belt layer 7 in the tire radial direction. The band layer 8 is composed of at least one band ply in which organic fiber cords are arranged at a small angle so as to be, for example, 10 degrees or less with respect to the tire circumferential direction. The band ply may be any of a jointless band formed by spirally winding a band cord or a ribbon-shaped band ply, or a spliced ply.

  The tread portion 2 is provided with a tread rubber Tg. As a preferred embodiment, the contour shape of the contact surface of the tread rubber Tg desirably draws a tread curve L whose radius of curvature decreases continuously or stepwise from the tire equator C toward the outer side in the tire axial direction. Such a tread curve L forms the surface of the tread portion 2 round, while making the sidewall region smaller. This is useful for increasing the rigidity of the side portion of the tire 1.

  The tread curve L is preferably an involute curve, for example. FIG. 2 shows an example of this involute curve. FIG. 2 shows an xy coordinate system in which the y-axis along the tire radial direction is set on the vertical axis and the x-axis along the tire axial direction is set on the horizontal axis. There, an ellipse V having a long axis ya is defined. The minor axis xa of the ellipse V is superimposed on the x axis, and one end of the minor axis xa coincides with the origin O. The involute curve is a trajectory drawn by the thread tip when the thread connecting the intersection CP of the tire equator C and the tread surface and the origin O is wound around the ellipse V while being fixed at the origin O. Can be represented. Such a tread curve L has a radius of curvature R (x) that continuously decreases as a function of x. Further, the tread curve L forms, for example, all or a part between the intersection CP and the tire maximum width position M of the sidewall portion 3.

  The tread curve L represents the contour shape of the contact surface of the tread rubber Tg in a normal state in which the tire 1 is assembled to the normal rim J, filled with the normal internal pressure, and unloaded. Here, the “regular rim” is a rim determined for each tire in a standard system including a standard on which a tire is based. For example, a standard rim for JATMA and a “Design Rim” for TRA. For ETRTO, “Measuring Rim”. The “regular internal pressure” is the air pressure defined by each standard 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” is TRA. The maximum value described in LIMITS AT VARIOUS COLD INFLATION PRESSURES is "INFLATION PRESSURE" if it is ETRTO, but it is uniformly 180 kPa if the tire is for passenger cars.

Further, as a particularly preferable aspect, it is preferable that the rigidity of the belt layer 7 is prevented from decreasing by gradually decreasing the thickness of the tread rubber Tg from the tire equator C toward the outer side in the tire axial direction. That is, when the thickness of the tread rubber Tg is made uniform, the belt layer 7 is curved with a large curvature along the tread curve L, and the lateral rigidity is likely to be lowered. For this reason, in this embodiment, the preferable aspect which makes the belt layer 7 exhibit sufficient lateral rigidity by controlling the thickness of the tread rubber Tg so as to satisfy the following formulas (1), (2) and (3). Show.
t1>t2> t3 (1)
0.60 × t1 ≧ t3 ≧ 0.10 × t1 (2)
t3 <6.0 (3)
Here, t1 is the thickness (mm) of the tread rubber at the tire equator C, t3 is the thickness (mm) of the tread rubber at the outer end 7e of the belt layer 7, and t2 is the outer end 7e of the belt layer 7. It is the thickness (mm) at an intermediate position with respect to the tire equator C. More preferably, the following formulas (2) ′ and (3) ′ are satisfied.
0.55 × t1 ≧ t3 ≧ 0.15 × t1 (2) ′
t3 <5.5 (3) ′

  In the run-flat tire 1 of this embodiment, side reinforcing rubber layers 9 are disposed on each of the sidewall portions 3 on both sides (however, only one side is shown in FIG. 1).

  In the present embodiment, the side reinforcing rubber layer 9 is disposed on the inner side in the tire axial direction of the carcass 6. The side reinforcing rubber layer 9 is formed in a substantially crescent shape as a whole by gradually reducing the thickness from the central portion 9a having the maximum thickness T toward the inner end 9i and the outer end 9o in the tire radial direction. Is done.

  The maximum thickness T of the side reinforcing rubber layer 9 is not particularly limited, but if it is too small, it is difficult to obtain a sufficient reinforcing effect, and conversely if too large, the weight of the tire may be increased. From such a viewpoint, the maximum thickness T is preferably 3 mm or more, more preferably 4 mm or more, and the upper limit is preferably 12 mm or less, more preferably 10 mm or less.

  The inner end 9 i of the side reinforcing rubber layer 9 is preferably located on the inner side in the tire radial direction than the outer end 10 T of the bead apex 10 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 terminates on the inner side in the tire radial direction of the belt layer 7, that is, 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 increase the longitudinal rigidity of the tire in a wide region of the sidewall portion 3, and at the same time, each end portion 9o and 9i is positioned in a region where the distortion during running is small to improve durability. Also useful for.

  In the present embodiment, the side reinforcing rubber layer 9 has a JIS durometer A hardness of preferably 65 ° or more, more preferably 70 ° or more, still more preferably 74 ° or more, and the upper limit is preferably 99. A rubber composition of less than or equal to, more preferably less than or equal to 90 degrees is suitable. When the JIS durometer A hardness of the side reinforcing rubber layer 9 is less than 65 °, the reinforcing effect on the sidewall portion 3 tends to be small, and conversely if it exceeds 99 degrees, the ride comfort during normal driving deteriorates. There is a tendency to invite.

  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, and acrylonitrile butadiene rubber are desirable. These can be used alone or in combination of two or more. 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 “VES F-3 type” manufactured by Iwamoto Seisakusho at a measurement temperature of 70 ° C., a frequency of 10 Hz, an initial elongation strain of 10%, and a half amplitude of 1%.

  In the run-flat tire 1 of the present embodiment, the side reinforcing cord layer 11 including at least one cord ply 11A in this example is disposed on each of the sidewall portions 3 on both sides. Each side reinforcing cord layer 11 extends in the tire radial direction between the outer end 11o in the tire radial direction and the inner end 11i in the tire radial direction. Accordingly, the side reinforcing cord layers 11 extending on the side wall portions 3 and 3 on both sides are not continuous with each other in the tread portion 2.

  During run flat running, the load borne by the inner region of the belt layer 7 is relatively small. Therefore, such a side reinforcing cord layer 11 can increase the longitudinal rigidity of the tire without reducing the load supporting ability during run-flat running and minimizing the increase in the weight of the tire. Further, the side reinforcing cord layer 11 can increase the bending rigidity of the side portion of the tire with a smaller increase in weight than when the side reinforcing rubber layer 9 is thickened or enlarged.

  Further, during run-flat running, tensile stress acts mainly on the outer surface of the side reinforcing rubber layer 9 in the tire axial direction, but the main body portion 6a of the folded ply 6A attached to the outer surface of the side reinforcing rubber layer 9. And the side reinforcing rubber layer 10 cooperates with each other to dramatically improve the tensile rigidity of the outer surface or the vicinity thereof. As a result, it is possible to reduce the amount of bending deformation of the side reinforcing rubber layer 9 during the run-flat running, thereby reducing the distortion of the sidewall portion 3 and suppressing the heat generation.

  The outer end 11o of the side reinforcing cord layer 11 is provided at a position sandwiched between the main body 6a of the folded ply 6A and the belt layer 7. Since this position is sandwiched between highly rigid plies, the distortion is relatively small even during run-flat travel. Therefore, damage starting from the outer end 11o is prevented, which helps to improve run-flat durability.

  When the outer end 11o of the side reinforcing cord layer 11 is too close to the outer end 7e of the belt layer 7, separation occurs at the outer end 11o of the side reinforcing cord layer 11 due to compressive strain acting on the outer end 7e of the belt layer 7. It tends to occur. On the contrary, when the outer end 11o of the side reinforcing cord layer 11 is far away from the outer end 7e of the belt layer 7 inward in the tire axial direction, the side reinforcing cord layer 11 does not have much effect even if it is reinforced. Many are placed and unnecessarily increase the weight of the tire. From such a viewpoint, the overlap length AL in the tire axial direction between the side reinforcing cord layer 11 and the belt layer 7 is preferably 5 mm or more, more preferably 10 mm or more, and further preferably 15 mm or more. Preferably, it is 40 mm or less, more preferably 30 mm or less, still more preferably 25 mm or less.

  The inner end 11i of the side reinforcing cord layer 11 is between the body portion 6a and the folded portion 6b of the folded ply 6A (more specifically, between the body portion 6a and the bead apex 10) and the bead core 5. It is provided in the vicinity position. Since this position is also a region where the strain during load running is relatively small, damage such as separation starting from the inner end 11 i of the side reinforcing cord layer 11 is prevented, and the durability of the tire 1 is enhanced.

  The “near the bead core 5” means a height range in which the radial distance S from the radial outer surface of the bead core 5 is 20 mm or less.

  When the inner end 11i of the side reinforcing cord layer 11 approaches the outer end 10T of the bead apex 10, strain concentration tends to occur there. From such a viewpoint, the overlap length RL in the tire radial direction between the bead apex 10 and the side reinforcing cord layer 11 is preferably 5 mm or more, more preferably 10 mm or more, and further preferably 15 mm or more. For example, 40 mm or less, preferably 30 mm or less is desirable from the viewpoint of tire weight.

  In FIG. 3, an example of the partial side view which saw through the side reinforcement cord layer 11 from the outer side surface is shown. In the present embodiment, the cord ply 11A of the side reinforcing cord layer 11 includes a cord 13 extending in the radial direction. The radial direction is a direction along the cut surface of the tire cross section including the tire rotation axis. Such a cord 13, like the folded ply 6A having a radial structure, can suppress strain during load running, and thus suppresses heat generation of the cord or the topping rubber covering the cord and improves fatigue resistance. To do.

  Further, the cord 13 of the cord ply 11A is preferably an organic fiber cord having a small specific gravity and excellent adhesion to rubber, particularly aramid, nylon, polyester, rayon or polyethylene-2,6-naphthalate (PEN). Organic fibers are preferred.

  As one embodiment, the same cord (polyester cord in this embodiment) as the folded ply 6A can be used for the cord ply 11A. In this case, since the cord material can be shared by the folded ply 6A and the side reinforcing cord layer 11, reinforcement of the run-flat tire 1 can be realized at a lower cost.

  As another embodiment, a cord having a higher modulus and higher heat resistance than the folded ply 6A can be used for the cord ply 11A. For example, when the folded ply 6A is made of a polyester cord, the cord ply 11A is preferably a rayon cord, an aramid cord, or a polyethylene-2,6-naphthalate (PEN) cord. The modulus of the cord is compared with 2% modulus at 20 ° C., and the heat resistance of the cord is compared with 2% modulus at 150 ° C., respectively.

  The side reinforcing cord layer 11 extends between the outer end 11o and the inner end 11i by drawing a smooth arc along the outer surface in the tire axial direction of the main body 6a. Although the inner side portion of the side reinforcing cord layer 11 in the tire radial direction can be along the outer surface of the bead apex 10, in this case, the compressive strain easily acts on the cord layer 11, so that the reinforcing effect is reduced. Easy to do.

  4 and 5 show another embodiment of the present invention. FIG. 4 is a right half sectional view of the tire in a normal state, and FIG. 5 is a partial side view of the side reinforcing cord layer 11 as viewed from the side.

  The run-flat tire 1 of this embodiment includes a plurality of cord plies 11A and 11B (two in this example) as the side reinforcing cord layers 11. The cords 13a and 13b of the cord plies 11A and 11B are inclined with respect to the reference line RL in the radial direction, and are overlapped so that the cords 13a and 13b intersect each other. That is, the side reinforcing cord layer 11 has a so-called cross-ply structure, maintains the rigidity of the sidewall portion 3 high, and contributes to improvement in steering stability. Thereby, the side reinforcement rubber layer 9 can be made thinner and the maximum thickness T can be significantly reduced.

  The angle of each cord 13a, 13b with respect to the radial direction is not particularly limited, but preferably 35 degrees or more, more preferably 45 degrees or more, and the upper limit is preferably 70 degrees or less, more preferably 60 degrees or less. What inclines at angle (theta) is desirable. When the angle θ is smaller than 35 degrees or larger than 70 degrees, the side reinforcing effect tends to be lowered and the run-flat performance is likely to deteriorate. The angle θ is measured at a substantially intermediate position in the tire radial direction of the reference line RL.

  In the present embodiment, the inner ends 11Ai and 11Bi and / or the outer ends 11Ao and 11Bo in the tire radial direction of the plies 11A and 11B are displaced from each other, thereby preventing formation of a large rigidity step. Preferably, as shown in FIG. 5, the length P of the radial displacement along the ply is 5 to 20 mm, more preferably about 8 to 15 mm.

  In the present embodiment, the outer end 11o of the side reinforcing rubber layer 11 and the outer end 9o of the side reinforcing rubber layer 9 are located away from each other. Similarly, the inner end 11 i of the side reinforcing rubber layer 11 and the inner end 9 i of the side reinforcing rubber layer 9 are located at a distance from each other. This also effectively suppresses the concentration of strain at each end.

  Further, in the side reinforcing cord layer 11 as shown in FIG. 4, the cord material may be different between the inner cord ply 11A disposed on the inner side in the tire axial direction and the outer cord ply 11B disposed on the outer side. it can. It is effective to make the modulus of the cord of the outer cord ply 11B arranged farther from the bending neutral line of the side reinforcing rubber layer 9 larger than that of the inner cord ply 11A. For example, a rayon cord can be used for the inner ply 11A and an aramid cord can be used for the outer ply 11B.

  As described above, the run-flat tire 1 according to the present embodiment can increase the run-flat travel distance while reducing the weight of the tire. 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.

  A run flat tire of 245 / 45R18 was prototyped based on the specifications in Table 1, and the run flat travel distance and tire weight were tested. For each tire, a belt layer made of two belt plies made of steel cord, a one-ply band layer made of aramid cord, and a carcass ply using a polyester cord were used as common specifications. Further, the side reinforcing rubber layer was unified in the tire radial arrangement region and the rubber composition (JIS durometer A hardness: 78 degrees), and the maximum thickness T was partially changed. The height ha of the bead apex was unified to 35 mm.

  The example tire was a run flat tire having the basic structure shown in FIGS. For comparison, a tire having the following configuration was also tested.

<Comparative Example 1>
As shown in FIG. 6, the only difference is that the side reinforcing cord layer is eliminated from the run-flat tire of FIG. 1, and the other points are the same as in FIG.

<Comparative example 2>
As shown in FIG. 7, the run-flat tire is based on the structure of Comparative Example 1, but the folded portion of the folded ply is extended to the inner side in the tire radial direction of the belt layer. The overlap length X1 shown in the figure is 20 mm. Side reinforcement cord layers are not provided. Other configurations are the same as those in FIG.

<Comparative Example 3>
As shown in FIG. 8, this is a run-flat tire in which one folded ply is added to the structure of Comparative Example 1. The folding height Y1 of the added folding ply is 20 mm.

<Comparative example 4>
This is a run-flat tire in which a flipper FP is added to the structure of Comparative Example 1 (FIG. 6). The specifications of the flipper FP are as follows.
Cord material: Aramid Cord angle: 45 °
Number of drives: 35 / 5cm
Height Y2: 15mm
Height Y3: 30mm

<Comparative Example 5>
This is a run-flat tire in which a filler FF is added to the structure of Comparative Example 1 (FIG. 6). The specifications of the filler FF are as follows.
Cord material: Aramid Cord angle: 45 °
Number of drives: 35 / 5cm
Height Y4: 12mm
Height Y5: 45mm

  The test method is as follows.

<Runflat mileage>
Each test tire was assembled to a rim (18 × 8 J) from which the valve core was removed, and an assembly with zero internal pressure was prepared. And each assembly was made to run with a drum test machine, and the running distance until a tire broke was measured. The traveling conditions were a speed of 90 km / h and a longitudinal load of 4.9 kN. Moreover, evaluation was displayed with the index | exponent which makes the driving distance of the comparative example 1 100. FIG. The larger the value, the better.

<Tire weight>
The weight per tire was measured and displayed as an index with the value of Comparative Example 1 being 100. The smaller the value, the lighter the weight.
Table 1 shows the test results.

It is sectional drawing of the run flat tire which shows embodiment of this invention. It is a diagram explaining an example of a tread curve. It is the expanded view seen from the side of a side reinforcement cord layer. It is sectional drawing of the run flat tire which shows other embodiment of this invention. It is the expanded view seen from the side surface of the side reinforcement cord layer of FIG. 3 is a cross-sectional view of a run flat tire of Comparative Example 1. FIG. 5 is a cross-sectional view of a run flat tire of Comparative Example 2. FIG. 6 is a cross-sectional view of a run flat tire of Comparative Example 3. FIG. 6 is a cross-sectional view of a run flat tire of Comparative Example 4. FIG. 6 is a cross-sectional view of a run flat tire of Comparative Example 5. FIG.

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 6A Folding ply 6a Folding ply main body part 6b Folding ply folding part 7 Belt layer 9 Side reinforcement rubber layer 10 Bead apex 11 Side reinforcement cord layer 11o Outer end 11i of side reinforcing cord layer Inner end of side reinforcing cord layer

Claims (5)

From a cord having a toroid-shaped main body part that extends from the tread part through the sidewall part to the bead core of the bead part, and a folded part that is connected to the main body part and folded back from the inside in the tire axial direction around the bead core. A carcass comprising at least one layer of folded ply,
A run-flat tire comprising a belt layer disposed on the outer side in the tire radial direction of the carcass and on the inner side of the tread portion, and a side reinforcing rubber layer having a substantially crescent cross section disposed on the sidewall portion,
A side reinforcing cord layer composed of at least one cord ply is disposed on the sidewall portion,
The side reinforcing cord layer includes an outer end in a tire radial direction sandwiched between a body portion of the folded ply and the belt layer,
A run-flat tire characterized by extending along the main body portion between the main body portion and the turned-up portion and between the inner end in the tire radial direction positioned in the vicinity of the bead core.   The run-flat tire according to claim 1, wherein an overlap length of the side reinforcing cord layer and the belt layer in the tire axial direction is 5 to 40 mm. The bead apex extending from the outer surface of the bead core to the outside in the tire radial direction is disposed between the bead portion and the body portion of the folded ply.
The side reinforcing cord layer extends between the bead apex and the main body,
The run-flat tire according to claim 1 or 2, wherein an overlap length in a tire radial direction between the bead apex and the side reinforcing cord layer is 5 to 40 mm.   The run-flat tire according to any one of claims 1 to 3, wherein the side reinforcing cord layer includes the same cord as the folded ply.   The run-flat tire according to any one of claims 1 to 3, wherein the side reinforcing cord layer includes a cord having a higher modulus and higher heat resistance than the folded ply.

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