JP2012126215A - Run flat tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve run flat durability while suppressing running resistance and noise.SOLUTION: The run flat tire 1 includes: a carcass 6 of a toroidal shape, which reaches the bead core 5 of a bead part 4 from a tread part 2 via a side wall part 3; a side reinforcement rubber layer 9 of a roughly crescent shape in a cross section, which is arranged inside the carcass 6 of the side wall part 3; and a side wall rubber 3G arranged in the outside of the carcass 6 of the side wall part 3 and forming a tire outer surface 3S. A slit 11 continuously extending to a tire circumferential direction is formed in the side wall rubber 3G. The slit 11 is closed in a normal load state in which a tire is rim-assembled to a normal rim J, the tire is filled with normal internal pressure, and the tire is loaded with a normal load. It is opened in the run flat state in which the internal pressure is zero, and to which the normal load is applied.

Description

  The present invention relates to a run-flat tire that can improve run-flat durability while suppressing running resistance and noise.

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

  However, even in the run-flat tire, the sidewall portion during the run-flat running is subjected to a large bending strain, and heat is generated with an increase in the running distance and / or speed, and the side reinforcing rubber layer is broken and the running becomes impossible. There is a case.

  Therefore, in recent years, a run flat tire in which a plurality of dimples are provided in the sidewall portion has been proposed (see, for example, Patent Document 1). Such a run-flat tire can increase the surface area of the sidewall portion by the dimples and can effectively promote heat dissipation to the atmosphere by generating turbulent flow around the surface of the sidewall portion of the running tire. .

JP 2009-298397 A

  However, in the run-flat tire as described above, the dimples in the sidewall portion generate turbulent flow even in a normal load state (normal driving) in which normal internal pressure is filled and a normal load is applied. There was a problem that resistance (fuel consumption) and noise increased.

  The present invention has been devised in view of the actual situation as described above, and is provided with a slit extending continuously in the tire circumferential direction in the sidewall rubber, the slit being opened in a normal load state and a run-flat state. The main object is to provide a run-flat tire capable of improving run-flat durability while suppressing running resistance and noise in a normal load state.

  The invention according to claim 1 of the present invention has a toroidal carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion. A run-flat tire comprising a side reinforcing rubber layer and a side wall rubber disposed on the outside of the carcass of the side wall portion and forming an outer surface of the tire, the side wall rubber being continuous in the tire circumferential direction A slit is formed, and the slit is closed in a normal load state where the rim is assembled to a normal rim and is filled with a normal internal pressure and a normal load is applied. It is characterized by opening in the run-flat state.

  According to a second aspect of the present invention, in the normal load application state, the slit is provided in a side reinforcing rubber layer projection region in which the side reinforcing rubber layer is projected onto the side wall rubber. It is a flat tire.

  According to a third aspect of the present invention, in the normal load state, the height in the tire radial direction from the bead base line to the slit is 0 of the maximum width height from the bead base line to the tire maximum width position. The run-flat tire according to claim 1 or 2, wherein the run-flat tire is 6 to 1.3 times.

  The invention according to claim 4 is the run flat tire according to any one of claims 1 to 3, wherein a maximum opening width of the slit is 6 to 12 mm in the run flat state.

  The invention according to claim 5 is the run flat tire according to any one of claims 1 to 4, wherein a minimum rubber thickness between the slit and the carcass ply is 2.0 to 3.0 mm. .

  According to a sixth aspect of the present invention, in the meridional section including the tire rotation axis in the normal load state and the run-flat state, the bottom of the slit is formed by an arc surface. It is the run flat tire of description.

  The invention according to claim 7 is the run flat tire according to claim 6, wherein the radius of curvature of the arc surface is 0.5 to 2.0 mm in the normal load state.

  In the invention according to claim 8, the inner surface in the tire axial direction of the side reinforcing rubber layer is provided with a concave groove continuous in the tire circumferential direction on the tire axial line extending from the bottom of the slit to the inner surface. A run-flat tire according to any one of claims 1 to 7.

  In the present specification, 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” for TRA. "Rim" or ETRTO means "Measuring Rim".

  The “regular internal pressure” is the air pressure defined by the standard for each tire. If JATMA, the maximum air pressure, if TRA, the maximum value described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” Then, “INFLATION PRESSURE” is set, but when the tire is for a passenger car, the pressure is uniformly set to 180 kPa.

  The “regular load” is a load determined by each standard 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” is set for TRA. The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “LOAD CAPACITY”.

  In the present specification, unless otherwise specified, the dimensions of each part of the tire are values specified in the ground contact center cross section in the normal load state.

  The run flat tire of the present invention includes a toroidal carcass that extends from the tread portion through the sidewall portion to the bead core of the bead portion, a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion, Side wall rubber disposed on the outside of the carcass of the side wall portion and forming the outer surface of the tire.

  In addition, a slit extending continuously in the tire circumferential direction is formed in the sidewall rubber. The slit is closed in a normal load state in which a normal rim is assembled and filled with a normal internal pressure and a normal load is applied, and is opened in a run-flat state in which the internal pressure is zero and a normal load is applied.

  In such a run-flat tire, in the run-flat state, slits are opened to increase the surface area of the sidewall portion, and turbulence is generated around the surface of the sidewall portion of the running tire to the atmosphere. Heat dissipation can be effectively promoted and run-flat durability can be improved. In addition, since the slit is closed in a normal load state, it is possible to prevent turbulent flow from occurring around the surface of the sidewall portion of the running tire and to suppress running resistance and noise.

It is sectional drawing which shows the run-flat tire of this embodiment. It is sectional drawing which shows the run flat state of FIG. (A) is sectional drawing which expands and shows the slit of a normal load load state, (b) is sectional drawing which expands and shows the slit of a run flat state. (A) is a partial side view of a run-flat tire in a run-flat state, and (b) is a partial side view of the run-flat tire in a normal load state. It is sectional drawing which shows a raw tire It is sectional drawing explaining a vulcanization molding process. It is sectional drawing which shows the run flat tire of other embodiment of this invention. It is sectional drawing which shows the run flat state of FIG. It is sectional drawing which shows the conventional run flat tire. It is sectional drawing which shows the run flat tire in which the dimple was formed in the sidewall part.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown 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, and the carcass 6 on the outer side in the tire radial direction. The belt layer 7 disposed on the inner side of the tread portion 2, the side reinforcing rubber layer 9 disposed on the inner side of the carcass 6 of each side wall portion 3, and the inner side of the carcass 6 or the side reinforcing rubber layer 9. A passenger car with an inner liner 10 is shown.

  The carcass 6 is composed of one or more radial structures in which carcass cords are arranged at an angle of, for example, 80 to 90 degrees with respect to the tire equator C, and in this embodiment, one carcass ply 6A. As the carcass cord, for example, an organic fiber cord such as polyester, nylon, rayon, or aramid, or a steel cord as necessary is adopted.

  The carcass ply 6A is folded back from the inner side to the outer side in the tire axial direction around the bead core 5 and the main body part 6a extending from the tread part 2 through the sidewall part 3 to the bead core 5 of the bead part 4. And a folded portion 6b. A bead apex rubber 8 made of hard rubber extending from the bead core 5 to the outside in the tire radial direction is disposed between the main body portion 6a and the folded portion 6b of the carcass ply 6A, and the bead portion 4 is appropriately reinforced.

  In the present embodiment, the folded portion 6b of the carcass 6 rolls up over the bead apex rubber 8 radially outward, and its outer end portion 6be is sandwiched between the main body portion 6a and the belt layer 7 and terminates. It has a so-called ultra-high turn-up folding structure. Thereby, the sidewall part 3 can be effectively reinforced by using one carcass ply 6A. Further, since the outer end portion 6be of the turned-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 belt layer 7 includes at least two belt plies 7A and 7B in which the belt cord is arranged at a small angle of, for example, 10 to 35 degrees with respect to the tire equator C. Are superimposed in the direction in which the cords cross each other. The belt cord of this embodiment employs a steel cord, but a highly elastic organic fiber cord such as aramid or rayon can also be used as necessary.

  The side reinforcing rubber layer 9 is continuously arranged in the tire circumferential direction on the inner side in the tire axial direction of the carcass 6 and on the outer side in the tire axial direction of the inner liner 10. In the side reinforcing rubber layer 9, the thickness r measured in the normal direction to the main body 6a of the carcass ply 6A gradually decreases from the center toward the inner end 9i and the outer end 9o in the tire radial direction. The cross section is formed in a substantially crescent shape.

  Further, the inner end 9 i of the side reinforcing rubber layer 9 is provided, for example, on the inner side in the tire radial direction than the outer end 8 t of the bead apex rubber 8 and on the outer side in the tire radial direction than the bead core 5. Thereby, the bending rigidity from the side wall part 3 to the bead part 4 improves with sufficient balance. Further, the outer end 9o of the side reinforcing rubber layer 9 is provided at a position on the inner side in the tire axial direction from the outer end 7e of the belt layer 7, for example. Thereby, the rigidity of buttress part B etc. is raised effectively.

  The length H1 in the tire radial direction between the inner end 9i and the outer end 9o of the side reinforcing rubber layer 9 is preferably, for example, about 35 to 70% of the tire cross-sectional height H2 from the bead base line BL. . The maximum thickness rt of the side reinforcing rubber layer 9 is preferably about 5 to 20 mm, for example, in the case of a passenger car tire. Further, the rubber hardness of the side reinforcing rubber layer 9 is desirably set to about 60 to 95 degrees, for example. With these configurations, the ride comfort and the side wall reinforcement effect can be achieved at a high level.

  The bead base line BL means a tire axial line passing through the rim diameter position of the normal rim J.

  In the present specification, the “rubber hardness” is a hardness according to durometer type A in an environment of 23 ° C. in accordance with JIS-K6253.

  The inner liner 10 is disposed in a toroid shape so as to straddle between the bead portions 4 and 4 in order to retain air in the tire lumen i, and forms a main portion of the tire lumen surface. For the inner liner 10, for example, a rubber composition having gas barrier properties such as butyl rubber, halogenated butyl rubber, and / or brominated butyl rubber is used.

  In the run-flat tire 1 according to the present embodiment, the slits 11 extending continuously in the tire circumferential direction are formed in the sidewall rubber 3G that is disposed outside the carcass 6 of the sidewall portion 3 and forms the tire outer surface 3S. The

  As shown in FIG. 3A, the slit 11 of the present embodiment includes, in a meridian cross section including a tire rotation axis, an outer side wall portion 12 </ b> A in the tire radial direction and an inner side wall portion in the tire radial direction facing this. 12B and the bottom 13 that smoothly connects between them.

  In the normal load loading state in which the slit 11 is assembled to the normal rim J (shown in FIG. 1) and is filled with the normal internal pressure and the normal load is applied, the slit 11 extends from the bottom 13 to the tire outer surface 3S. The outer side wall portion 12A and the inner side wall portion 12B extend while decreasing the separation distance W1 in the tire radial direction. Accordingly, the slit 11 includes an outer protruding corner portion 14A where the outer side wall portion 12A and the tire outer surface 3S intersect, and an inner protruding corner portion 14B where the inner side wall portion 12B and the tire outer surface 3S intersect. At least abuts and closes at the tire outer surface 3S in the tire circumferential direction.

  Further, in the slit 11 of the present embodiment, the outer protruding corner portion 14A and the inner protruding corner portion 14B come into contact with each other to close the opening, so that the outer side wall portion 12A and the inner side wall portion 12A are inward of the side wall rubber 3G. A drop-like space 15 surrounded by the side wall portion 12B and the bottom portion 13 and extending in a tapered manner toward the tire outer surface 3S is formed.

  In addition, as shown in FIGS. 2 and 3 (b), the slit 11 is formed in the vicinity of the ground center cross section in the run-flat state in which the internal pressure is zero and a normal load is applied. Due to the large deflection, the contact between the outer protruding corner portion 14A and the inner protruding corner portion 14B is released, and the outer side wall portion 12A and the inner side wall portion 12B are greatly separated in the tire radial direction. Thereby, the slit 11 opens in the tire outer surface 3S.

  With this opening, the slit 11 of the present embodiment is formed in a tapered groove shape in which the distance W1 between the outer side wall portion 12A and the inner side wall portion 12B gradually decreases from the tire outer surface 3S to the bottom portion 13.

  Such a run-flat tire 1 increases the surface area of the sidewall portion 3 by exposing the outer sidewall portion 12A, the inner sidewall portion 12B, and the bottom portion 13 through the opening of the slit 11 in the run-flat state. be able to. Thereby, the slit 11 can dissipate the heat of the side wall part 3 which arises by the big bending distortion at the time of run flat driving | running | working effectively to air | atmosphere.

  In addition, since unevenness is formed in the sidewall portion 3 due to the opening of the slit 11, as shown in FIG. 4A, a turbulent flow S is generated around the surface of the sidewall portion 3 of the running tire. Can be generated. By this turbulent flow, the air can smoothly flow into the slit 11 and the heat of the sidewall portion 3 can be dissipated more effectively. Such a run flat tire 1 can suppress the breakage of the side reinforcing rubber layer 9 (shown in FIG. 2) and the like, and can improve the run flat durability.

  Furthermore, in the run flat tire 1 of the present embodiment, part of the increase in the run flat durability can be used to reduce the volume of the side reinforcing rubber layer 9, while ensuring the necessary run flat durability. It is also possible to suppress an improvement in comfort and an increase in tire mass.

  Further, as shown in FIG. 1 and FIG. 3A, the slit 11 is closed at the tire outer surface 3S in the normal load application state during normal running, so that the tire outer surface 3S of the sidewall portion 3 is closed. Can be formed substantially flush with each other. Therefore, the run-flat tire 1 prevents the turbulent flow S (shown in FIG. 4A) from occurring around the surface of the sidewall portion 3, as shown in FIG. (Wind noise) can be suppressed.

  Furthermore, the slit 11 is formed with a tapered space 15 toward the outer surface 3S of the tire in a normal load state, so that it can exhibit a buffering function when abruptly overcoming a protrusion and improve riding comfort. .

  As shown in FIGS. 3A and 3B, the bottom portion 13 is preferably formed by an arcuate surface 13S in the normal load application state and the run flat state. Such a circular arc surface 13 </ b> S can suppress the generation of cracks and cracks by dispersing strains that tend to concentrate on the bottom 13.

  In order to effectively exhibit such an action, as shown in FIG. 3A, in the normal load application state, the radius of curvature R1 of the circular arc surface is preferably 0.5 mm or more, more preferably 0.8mm or more is desirable. If the radius of curvature R1 is too small, there is a possibility that the above distortion cannot be sufficiently dispersed. Conversely, if the radius of curvature R1 is too large, the separation distance W1 becomes excessively large, and there is a possibility that the mouth cannot be closed in the normal load application state. From such a viewpoint, the curvature radius R1 is preferably 2.0 mm or less, more preferably 1.8 mm or less.

  In the normal load application state, the maximum depth D1 of the slit 11 is preferably 2.0 mm or more, and more preferably 2.5 mm or more. If the maximum depth D1 is too small, the slit 11 may not be able to be opened with a sufficient size in the run-flat state. Conversely, if the maximum depth D1 is too large, there is a possibility that the mouth cannot be closed sufficiently. From such a viewpoint, the maximum depth D1 is preferably 4.0 mm or less, and more preferably 3.5 mm or less.

  As shown in FIG. 1, the slit 11 is preferably provided in a side reinforcing rubber layer projection region T obtained by projecting the side reinforcing rubber layer 9 onto the side wall rubber 3G in the normal load state. Thereby, the slit 11 can effectively dissipate the heat of the side reinforcing rubber layer 9 that generates a large amount of heat during run-flat travel to the atmosphere.

  The “side reinforcing rubber layer projection region T” includes the intersection To of the straight line L1 extending in the tire axial direction from the outer end 9o of the side reinforcing rubber layer 9 to the tire outer surface 3S and the tire outer surface 3S, and the inner end 9i. A region of the tire outer surface 3S sandwiched by an intersection Ti between a straight line L2 extending in the tire axial direction from the tire outer surface 3S and the tire outer surface 3S.

  In order to dissipate the heat of the side reinforcing rubber layer 9 more effectively, the height H3 in the tire radial direction from the bead base line BL to the slit 11 in the normal load state is the tire maximum from the bead base line BL. The maximum width height H4 up to the significant position M is preferably 0.6 times or more, more preferably 0.7 times or more. If the height H3 is too small, the slit 11 is formed on the inner end 9i side from the center of the side reinforcing rubber layer 9 that generates a large amount of heat, and may not be sufficiently dissipated. Conversely, if the height H3 is too large, the slit 11 may be formed on the outer end 9o side of the side reinforcing rubber layer 9. From such a viewpoint, the height H3 is preferably 1.3 times or less, more preferably 1.2 times or less of the maximum width height H4.

  As shown in FIG. 3B, the maximum opening width W3 of the slit 11 is preferably 6 mm or more, and more preferably 8 mm or more in the ground flat cross section of the run-flat state. If the maximum opening width W3 is too small, the heat of the sidewall portion 3 may not be sufficiently dissipated. On the contrary, if the maximum opening width W3 is too large, the slit 11 may not be sufficiently closed in a normal load state. From such a viewpoint, the maximum opening width W3 is preferably 12 mm or less, and more preferably 10 mm or less.

  The minimum rubber thickness W4 between the slit 11 and the carcass ply 6A (carcass cord) is preferably 2.0 mm or more, more preferably 2.2 mm or more. If the minimum rubber thickness W4 is too small, cracks that reach the carcass ply 6A starting from the slit 11 may easily occur. On the other hand, if the minimum rubber thickness W4 is too large, the heat of the side reinforcing rubber layer 9 may not be sufficiently dissipated. From such a viewpoint, the minimum rubber thickness W4 is preferably 3.0 mm or less, more preferably 2.8 mm or less.

Next, an embodiment of a method for manufacturing the run flat tire 1 will be described.
The run-flat tire 1 of the present embodiment can be manufactured including a step of molding the raw tire 1L and a step of vulcanizing the raw tire 1L, as shown in FIGS.

  In the step of forming the green tire, as shown in FIG. 5, a tire frame including a carcass 6 having a bead core 5 and a belt layer 7 is formed on a tread rubber 2G, sidewall rubber 3G, clinch rubber 4G, and side reinforcing rubber 9G. And the raw tire (green tire) 1L to which the inner liner rubber 10G is attached is formed. In the state of the raw tire 1L, the slit 11 (shown in FIG. 1) is not yet formed.

  In the vulcanization step, as shown in FIG. 6, the raw tire 1L is vulcanized using a vulcanization mold 21 having a cavity 21s that forms the outer surface of the raw tire 1L.

  The vulcanization mold 21 of the present embodiment includes, for example, a pair of sidewall molding dies 22 having a sidewall molding surface 22s, a tread molding dies 23 having a tread rubber molding surface 23s, and a bead portion 4 of the raw tire 1L. A pair of bead rings 24 that can be held.

  In the vulcanization mold 21, the cavity 21s is formed by fitting the sidewall mold 22, the tread mold 23, and the bead ring 24 together. The raw tire 1L disposed in the cavity 21s is vulcanized and pressed against the cavity 21s by the expansion of the bladder 25 to which a high-pressure fluid is supplied in accordance with the conventional practice.

  In order to form the slit 11, a protruding piece 26 extending continuously in the tire circumferential direction is provided on the sidewall molding surface 22 s of the sidewall molding die 22. In the sidewall rubber 3G pressed by the protruding piece 26, the slit 11 is formed as an inverted pattern of the protruding piece 26. The projecting piece 26 is formed to have a larger width toward the inner side in the tire axial direction. However, the side wall rubber 3G is separated from the width of the slit 11 by releasing the side wall molding die 22 toward the outer side in the tire axial direction. It is elastically deformed in the direction of spreading and can be easily removed. Further, the width in the tire axial direction between the sidewall molding surfaces 22s and 22s is larger than the width of the outer surface of the sidewall portion 3 of the tire 1 in the normal state in which the tire is rim-assembled and filled with the normal internal pressure and filled with the normal internal pressure. By setting it small, the slit 11 can be more easily closed in the normal state.

FIG. 7 shows a run flat tire 1 according to another embodiment of the present invention.
The run-flat tire 1 according to the present embodiment has a recess that is continuous in the tire circumferential direction on a tire axial direction line L3 drawn from the bottom 13 of the slit 11 to the inner surface 9s on the inner surface 9s of the side reinforcing rubber layer 9 in the tire axial direction. A groove 31 is provided. The concave groove 31 includes a groove wall portion 31a on the outer side in the tire radial direction, a groove wall portion 31b on the inner side in the tire radial direction that faces the groove wall portion 31a, and a groove bottom portion 31c that connects between them in an arc shape.

  Further, in the groove 31 of the present embodiment, the outer groove wall portion 31a and the inner groove wall portion 31b are separated from each other and the groove width W7 is the inner surface of the side reinforcing rubber layer 9 in the regular load state. It has a groove cross section that decreases from 9s toward the groove bottom 31c. The groove 31 has a groove width W7 on the inner surface 9s of about 3.0 to 15.0 mm and a groove depth D3 of about 1.0 to 5.0 times the groove width W7. Such a recessed groove 31 can follow the unevenness of the road surface and can easily bend the sidewall portion 3 in a direction to close the groove, so that a good riding comfort can be obtained.

  Further, as shown in FIG. 8, the concave groove 31 closes the groove width W7 (shown in FIG. 8) during the run-flat running, and the side reinforcing rubber layer 9 has a substantially crescent-shaped cross section. Stiffness can be increased. Therefore, during run flat running, the longitudinal deflection of the tire is effectively suppressed, and as a result, a long continuous running distance can be obtained.

  Moreover, the recessed groove 31 can bend | curve large locally the side wall part 3 by which the slit 11 is distribute | arranged by closing the groove width W7 (shown in FIG. 8). This curvature of the side wall portion 3 can effectively increase the surface area of the side wall portion 3 by effectively opening the slits 11 and improve the run flat durability.

  In order to manufacture the run-flat tire 1 having such a groove 31, a protrusion (not shown) for forming the groove 31 is provided on the outer surface of the bladder 25 shown in FIG. By providing a convex portion on the core, it can be easily formed during vulcanization molding.

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

Run-flat tires having the basic structure shown in FIG. 1 or 7 and having the slits shown in Table 1 were manufactured, and their performance was evaluated. For comparison, the conventional run flat tire without slits shown in FIG. 9 (Comparative Example 1) and the dimples (diameter: 8.0 mm, depth: 2.0 mm) on the side wall shown in FIG. The formed run flat tire (Comparative Example 2) was similarly tested. The common specifications are as follows.
Tire size: 245 / 40RF18
Rim size: 18 × 8.5J
Tire cross-section height H2: 98mm
Maximum width H4: 49mm
Side reinforcement rubber layer
Length H1: 55mm
Ratio (H1 / H2): 56%
Groove:
Groove width W7: 8.0mm
Groove depth D3: 6.0 mm
Ratio (D3 / W7): 0.75 times The test method is as follows.

<Surface temperature of sidewall during run-flat running>
Each test tire was assembled on the rim from which the valve core was removed, and a drum with a load of 4.15 kN and a speed of 80 km / h was run for 80 km at a speed of 80 km / h using a drum tester with zero internal pressure. The surface temperature of the sidewall portion at the tire maximum width position was measured. The lower the number, the better.

<Runflat durability>
Each test tire was assembled on the rim from which the valve core had been removed, and the test was carried out by the step speed method in accordance with the load / speed performance test defined by ECE30 using a drum tester in a state where the internal pressure was zero. The test increased the running speed sequentially and measured the speed and time when the tire broke down. Evaluation was made with an index with Comparative Example 1 as 100. The higher the number, the better.

<Tire mass>
The mass per tire was measured, and the reciprocal thereof was displayed as an index with Comparative Example 1 as 100. A smaller index is better.

<Vertical spring coefficient>
Each test tire was assembled on the rim, filled with an internal pressure of 230 kPa, grounded on a flat surface with a load of 4.15 kN, and the amount of vertical deflection of the tire was measured. Then, the longitudinal spring constant was approximately obtained by dividing the load of 4.15 kN by the amount of vertical deflection. The results were expressed as an index with Comparative Example 1 as 100. The smaller the numerical value, the smaller the vertical spring, and the better the riding comfort.

<Ride comfort>
Each test tire was assembled on the rim, filled with 230 kPa of internal pressure, mounted on all wheels of a domestic FF vehicle with a displacement of 4000 cc, and run on stepped roads, Belgian roads and Bitzmann roads on dry asphalt surfaces . Then, the rough feeling, push-up and damping were comprehensively evaluated by the driver's sensation, and the comparative example 1 was displayed as a score of 100. The larger the value, the better.

<Running resistance (fuel efficiency)>
Each test tire was assembled on the rim under the above conditions and mounted on the vehicle. The test tire on the dry asphalt road surface was run for 50 km, and the travel distance per liter of fuel consumption was determined. The results were expressed as an index with Comparative Example 1 as 100. The smaller the value, the lower the running resistance and the better.

<Noise resistance>
Each test tire is assembled to the rim under the above conditions and mounted on the vehicle, and a test course on a dry asphalt road surface is run at a speed of 80 km / h. The overall noise level dB (A) was measured at position. Evaluation was made with an index with Comparative Example 1 as 100. The smaller the value, the smaller the noise and the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the run-flat tire of the example can improve the run-flat durability while suppressing running resistance and noise.

DESCRIPTION OF SYMBOLS 1 Run flat tire 2 Tread part 3 Side wall part 3G Side wall rubber 3S Tire outer surface 4 Bead part 5 Bead core 6 Carcass 9 Side reinforcement rubber layer 9
11 Slit

Claims (8)

A toroid-like carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a side-reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion, and the sidewall portion A run flat tire provided with a sidewall rubber disposed outside the carcass and forming the outer surface of the tire,
The sidewall rubber is formed with a slit extending continuously in the tire circumferential direction,
The slit is closed in a normal load state in which a normal rim is assembled and a normal internal pressure is filled and a normal load is applied, and the slit is opened in a run flat state in which the internal pressure is zero and a normal load is applied. Run-flat tire characterized by.   2. The run-flat tire according to claim 1, wherein, in the normal load application state, the slit is provided in a side reinforcing rubber layer projection region in which the side reinforcing rubber layer is projected onto the side wall rubber.   In the normal load application state, the height in the tire radial direction from the bead base line to the slit is 0.6 to 1.3 times the maximum width height from the bead base line to the tire maximum width position. Item 3. The run-flat tire according to item 1 or 2.   The run flat tire according to any one of claims 1 to 3, wherein a maximum opening width of the slit is 6 to 12 mm in the run flat state.   The run flat tire according to any one of claims 1 to 4, wherein a minimum rubber thickness between the slit and the carcass ply is 2.0 to 3.0 mm.   The run flat tire according to any one of claims 1 to 5, wherein a bottom portion of the slit is formed by an arc surface in a meridian cross section including a tire rotation axis in the normal load application state and the run flat state.   The run-flat tire according to claim 6, wherein a radius of curvature of the arc surface is 0.5 to 2.0 mm in the normal load state.   The inner surface in the tire axial direction of the side reinforcing rubber layer is provided with a concave groove continuous in the tire circumferential direction on a tire axial line extending from the bottom of the slit to the inner surface. The described run-flat tire.

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