JP5185599B2 - Run flat tire - Google Patents

Description

  The present invention relates to a run-flat tire that can continue running at a constant speed even when punctured, and more particularly to a run-flat tire that can improve ride comfort and durability without significant increase in mass.

  Conventionally, as shown in FIG. 9, even when tire air escapes due to puncture or the like, the vehicle travels continuously at a relatively high speed for a certain distance (hereinafter, such travel is referred to as “run-flat travel”). A known run-flat tire b is known (see Patent Documents 1 and 2 below). In such a run-flat tire b, a reinforcing rubber layer c having a substantially crescent-shaped cross section is provided on the sidewall portion, and the sidewall portion whose rigidity is enhanced by the reinforcing rubber layer c acts on the tire instead of the air pressure. Substantially support the load. As a result, the vertical deflection of the tire is minimized, and as a result, run-flat running is possible.

  By the way, during the run-flat running, the tread portion d receives a large compressive force in the width direction as the side wall portions on both sides are bent, and the crown portion d1 is greatly bent inward in the tire radial direction. When such a large deflection of the crown portion d1 is repeated for a long time, the rubber and the cord are easily peeled off at the tread portion.

  Further, based on the above-described bending, the tire b is grounded only at the shoulder portions d2 that are both sides of the crown portion d1. Such traveling increases the contact pressure of the shoulder portion d2 and promotes heat generation and wear at the shoulder portion d2. Then, for example, a crack may occur at the edge of the belt layer e, which may grow and cause destruction of the tire.

  In order to suppress such bending of the crown portion d1, it can be considered that the thickness T of the tread rubber is increased to increase the compression resistance. However, with this method, the distance between the belt layer e and the road surface on the ground contact surface during normal running increases, and as a result, the steering stability tends to deteriorate, for example, the responsiveness during turning is deteriorated.

  The present applicant has already proposed the following Patent Document 3 in order to suppress the bending of the crown part d1 described above. This proposal teaches that a reinforcing rubber layer is disposed between the belt layer and the carcass in the tread portion d. However, since the entire reinforcing rubber is composed of one type of rubber, it is not possible to give different characteristics to the crown portion d1 and the shoulder portion d2, and further improvement in durability and the like can be achieved. There is room.

JP 2002-301911 A Japanese Patent No. 2999489 JP 2002-12004 A

  The present invention has been devised in view of the above problems, and uses an aramid fiber cord having high elasticity for a carcass cord and disposing an insulation rubber between the carcass and the belt layer. Basically, the main object is to provide a run-flat tire that can improve steering stability and durability during run-flat travel without significantly increasing the tire mass.

The invention according to claim 1 of the present invention includes a carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, and a belt layer disposed inside the tread portion and radially outside the carcass, A run-flat tire comprising a side reinforcing rubber layer having a substantially crescent-shaped cross section disposed inside the carcass of the sidewall portion, wherein the carcass is arranged at an angle of 45 to 90 ° with respect to the tire equator. The carcass ply is made of an aramid fiber having a twist coefficient T of 0.5 to 0.7 represented by the following formula (1), and the carcass and the belt. Between the layers, there is an insulation rubber extending in the tire axial direction, and the insulation rubber is arranged in the center of the tread. And Ungomu unit, at least comprising a formulation different pair of shoulder rubber portions and their disposed on both outer sides in the tire axial direction and the crown rubber portion, based on JIS-K6253 was measured at a temperature 23 ° C. of the crown rubber portion a hardness by durometer type a is 70 to 99 degrees, and the hardness and a loss tangent tanδ of the shoulder rubber portions is characterized by less than the hardness and a loss tangent tanδ of the crown rubber portion.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
However, N is the number of twists (times / 10 cm), D is the total display decitex (fineness) of the cord, and ρ is the specific gravity of the cord material.

The invention of claim 2, wherein the loss tangent tan of the crown rubber portion is 0.15 to 0.25, and wherein the hardness Moreover the loss tangent tanδ less than 50 degrees and 70 degrees of shoulder rubber portion The run-flat tire according to claim 1, which is 0.04 to 0.12.

  According to a third aspect of the invention, the belt layer includes a plurality of belt plies stacked in the tire radial direction, and the width of the insulation rubber in the tire axial direction is the outermost in the tire radial direction. The run-flat tire according to claim 1 or 2, which is 90 to 110% of a width in the tire axial direction of the arranged belt ply.

  According to a fourth aspect of the present invention, the belt layer is composed of a plurality of belt plies stacked in the tire radial direction, and the width of the crown rubber portion in the tire axial direction is the outermost in the tire radial direction. The run-flat tire according to any one of claims 1 to 3, which is 60 to 85% of a width in a tire axial direction of the arranged belt ply.

  A fifth aspect of the present invention is the run flat tire according to any one of the first to fourth aspects, wherein the thickness of the insulation rubber is 2.0 to 10.0 mm.

  The invention according to claim 6 is the run-flat tire according to any one of claims 1 to 5, wherein the twist coefficient T of the carcass cord is 0.6 to 0.7.

  The invention according to claim 7 is the pneumatic tire according to any one of claims 1 to 6, wherein the topping rubber of the carcass ply has a complex elastic modulus E * t of 5 to 13 MPa.

The invention according to claim 8 is a tire meridian cross section including a tire rotation axis in a normal unloaded state in which a normal rim is assembled and a normal inner pressure is filled, and 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 7, 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
Here, Y60, Y75, Y90, and Y100 represent 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 tire outer surface which are separated from each other and the intersection (CP), and H is the tire cross-sectional height.

Further, the loss tangent and the complex elastic modulus are values measured using a viscoelastic spectrometer under the following conditions in accordance with JIS-K6394.
Initial strain: 10%
Amplitude: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 °

  In the run flat tire of the present invention, an aramid fiber cord particularly excellent in heat resistance is used as a carcass cord. Therefore, carcass cord damage due to temperature rise during run-flat traveling can be suppressed. In addition, since the aramid fiber cord is highly elastic and can increase the load support capability, the amount of vertical deflection of the tire during run-flat running can be reduced while reducing the number of carcass plies (lightening). In addition, such a highly elastic carcass cord can suppress the bending of the tread center portion inward in the radial direction during run-flat running, thereby reducing heat generation at the tread shoulder portion.

  The run-flat tire of the present invention has an insulation rubber extending in the tread width direction between the carcass and the belt layer. In this insulation rubber, the crown rubber portion disposed in the center portion of the tread is formed of a hard rubber having a relatively high resistance to compressive stress, while both outer sides of the crown rubber portion in the tire axial direction are formed. The pair of shoulder rubber portions disposed on the rubber is formed of rubber having a relatively low heat generation property than the crown rubber portion. Such a run-flat tire further suppresses the bending of the tread central portion in the radial direction and the heat generation at the tread shoulder portion during the run-flat running by the synergistic action with the carcass cord of the aramid fiber. Can be reduced.

  Therefore, the run flat tire of the present invention can further enhance the run flat durability. In addition, steering stability during run-flat running can be improved, and high speed and long distance can be achieved during run-flat running.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a run-flat tire 1 according to this embodiment in a normal no-load state, FIG. 2 is an enlarged view of a main part of the tread portion, and FIG. Sectional views of the tire 1 in a run-flat state are respectively shown. Unless otherwise specified, the dimensions of each part of the tire are the values in the normal no-load state.

  Here, the “regular no-load state” refers to a no-load state in which the run-flat tire 1 is assembled to the regular rim J and filled with the regular internal pressure.

  In addition, 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, “Design Rim” for TRA, For ETRTO, use “Measuring Rim”. Furthermore, the “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” is TRA. The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO, but 180 kPa for tires for passenger cars. Furthermore, 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 value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  The run-flat tire 1 includes a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, and a belt layer 7 disposed outside the carcass 6 in the tire radial direction and inside the tread portion 2. A bead apex rubber 8 that tapers outward from the outer surface of the bead core 5 in the radial direction of the tire, and a side having a substantially crescent shape in cross section disposed on at least a part of the inside of the carcass 6 and the side wall portion 3. The reinforcing rubber layer 9 is disposed between the carcass 6 and the belt layer 7, the inner liner rubber 10 made of rubber having a gas barrier property disposed on the inner side in the tire axial direction of the side reinforcing rubber layer 9 in this embodiment. Insulation rubber 11 is included.

  The carcass 6 is formed of at least one carcass ply 6A having a carcass cord arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator C, in this embodiment, one carcass ply 6A. The carcass ply 6A includes a toroidal main body portion 6a extending between the bead cores 5 and 5 and a pair of folded back portions that are provided on both sides of the bead core 5 and are folded from the inner side to the outer side in the tire axial direction. Part 6b.

  The bead apex rubber 8 is disposed between the main body portion 6a and the folded portion 6b of the carcass ply 6A. The bead apex rubber 8 is made of a relatively hard rubber, for example, having a hardness of 65 to 95 degrees or more, more preferably 70 to 90 degrees, thereby increasing the bending rigidity of the bead portion 4 and thus improving the handling stability. To help. In addition, in this specification, the hardness of rubber means the hardness by durometer type A based on JIS-K6253 measured at the temperature of 23 degreeC.

  The height ha in the tire radial direction from the bead base line BL to the outer end 8t of the bead apex rubber 8 is not particularly limited, but if it is too small, the steering stability in the run-flat state tends to be lowered. From such a viewpoint, the height ha is preferably 20% or more of the tire cross-section height H, more preferably 25% or more. On the other hand, if the height ha is too large, the ride comfort may be deteriorated. Therefore, it is preferably 50% or less, more preferably 45% or less of the tire cross-section height H.

  In the present embodiment, the folded portion 6b of the carcass ply 6A extends beyond the outer end 8t of the bead apex rubber 8 outward in the tire radial direction, and the outer end portion 6be is between the main body portion 6a and the belt layer 7. It is in the position between. Thereby, the side wall part 3 is effectively reinforced by a small number of carcass plies 6A.

  The belt layer 7 is formed by overlapping a plurality of belt plies having belt cords (steel cords in the present embodiment) arranged at an angle of, for example, 10 to 35 ° with respect to the tire equator C in the tire radial direction. . In this embodiment, the belt layer 7 is composed of two belt plies 7A and 7B that are stacked with the width center aligned.

  The width of the belt layer 7 (in this example, the width between the outer ends 7e of the wide belt ply 7A) BWi is preferably 0.70 to 0.95 times the tire maximum width SW. Such a belt layer 7 can provide a tagging effect over almost the entire region of the tread portion 2 and can effectively maintain the profile of the outer surface of the tire. Further, the belt ply 7B arranged on the outermost side in the tire radial direction is formed such that the width BWo (shown in FIG. 2) in the tire axial direction is approximately 90 to 98% of the width BWi of the belt layer. desirable. As a result, it is possible to prevent a large rigidity step from occurring due to the outer ends of the belt plies 7A and 7B overlapping.

  Here, the tire maximum width SW is a tire axial distance between the tire maximum width points M and M. Further, the tire maximum width point M is determined from the tire cross-sectional contour shape excluding characters, patterns, rim protectors, and the like provided on the sidewall portion 3, and specifically, substantially the point m forming the maximum width of the carcass 6. Are at the same height.

  The side reinforcing rubber layer 9 has a substantially crescent cross section in which the thickness is gradually reduced from the central portion 9a toward the inner end 9i and the outer end 9o in the tire radial direction and smoothly curved along the sidewall portion 3. It is formed in a shape and extends continuously in the tire circumferential direction. Of course, the side reinforcing rubber layer 9 is provided on each side wall portion 3.

  In the present embodiment, the inner end 9 i of the side reinforcing rubber layer 9 is provided 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 is improved with good balance. In particular, the length Wi in the tire radial direction of the overlapping portion between the side reinforcing rubber layer 9 and the bead apex rubber 8 is preferably 5 to 50 mm.

  Further, the outer end 9o of the side reinforcing rubber layer 9 extends, for example, to the inner side of the tread portion 2, and is provided on the inner side in the tire axial direction from the outer end 7e of the belt layer 7 in this embodiment. Thereby, the rigidity of a buttress part etc. is improved effectively. In particular, the length Wo in the tire axial direction of the overlapping portion between the side reinforcing rubber layer 9 and the belt layer 7 is preferably larger than 0 mm and not larger than 50 mm.

  The length L in the tire radial direction between the inner end 9i and the outer end 9o of the side reinforcing rubber layer 9 (that is, the length in the tire radial direction of the side reinforcing rubber layer 9) is not particularly limited. The reinforcement effect on the part 3 tends to be reduced, and on the contrary, even if it is too large, the riding comfort and rim assemblability during normal running tend to be deteriorated. From such a viewpoint, the length L is preferably 35% or more, more preferably 40% or more of the tire cross-section height H, and preferably 70% or less, more preferably 65% or less.

  The maximum thickness tc of the side reinforcing rubber layer 9 can be appropriately determined according to the applied load and the tire size. However, if it is too small, it is difficult to obtain the effect of reinforcing the sidewall portion 3. From such a viewpoint, the maximum thickness tc is preferably 5 mm or more, more preferably 8 mm or more. On the other hand, if the thickness tc is too large, the tire mass may increase and excessive heat generation may occur. Therefore, the thickness tc is preferably 20 mm or less, more preferably 15 mm or less.

  In order to suppress the longitudinal deflection of the tire during run-flat running, the hardness of the side reinforcing rubber layer 9 is preferably 30 degrees or more, more preferably 40 degrees or more, and further preferably 60 degrees or more. On the other hand, if the 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 90 degrees or less, more preferably 85 degrees or less. Is desirable.

  In the run flat tire 1 as described above, in the present invention, first, an aramid fiber is employed for the carcass cord in order to improve the handling stability and durability during the run flat running.

  The aramid fiber is known as a highly elastic fiber, and can be used for the carcass cord of the run-flat tire 1 to increase the load supporting ability of the tire. Therefore, for example, the tire deformation during the run-flat running can be reduced while reducing the weight of the tire by reducing the number of carcass plies, reducing the diameter of the carcass cord, and / or reducing the cord arrangement density (number of cord ends). Moreover, the aramid fiber has a characteristic that the decrease in elastic modulus is small compared to other organic fiber cord materials even at a high temperature of 100 to 150 ° C. and is excellent in heat resistance. Accordingly, it is possible to prevent the carcass cord from being reduced in strength and causing damage due to an increase in tire temperature during run-flat running, or an increase in the amount of tire deformation due to a decrease in elastic modulus and an accompanying further increase in tire temperature. . As a result, run flat durability can be improved. Further, even when the tire temperature rises, the tire rigidity can be increased while maintaining a high elastic modulus, so that the steering stability during run-flat can be improved.

  On the other hand, aramid fibers tend to have poor fatigue resistance due to their high elastic modulus. Therefore, in this embodiment, as schematically shown in FIG. 4, two filament bundles 21 (ie, strands 21) of an aramid fiber twisted on the carcass cord 20 are further twisted together by an upper twist. A twisted structure is adopted, and the twisting at this time is performed with a higher twisting coefficient T than in the past.

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

  And by increasing the twist coefficient T to a range of 0.5 to 0.7, it is possible to improve the fatigue resistance, which is a defect of the aramid fiber cord, and the run-flat durability is higher than that of the conventional rayon cord. Can be greatly improved. If the twist coefficient T of the carcass cord 20 is less than 0.5, the effect of improving the fatigue resistance is small and the run-flat durability cannot be sufficiently increased. On the contrary, when the twist coefficient T exceeds 0.7, it becomes difficult to twist the cord, which is disadvantageous for productivity. In particular, the lower limit of the twist coefficient T is preferably 0.6 or more, whereby the fatigue resistance of the cord can be further improved, and the run-flat durability can be further improved.

  In the carcass cord 20, a two-strand structure is desirably employed in order to exert an excellent reinforcing effect by utilizing the high elasticity that is an important characteristic of the aramid fiber. At that time, a so-called balance twist in which the number of lower twists and the number of upper twists are equal is preferable, but the ratio of the number of twists (number of lower twists / number of upper twists) is in the range of 0.2 to 2.0, preferably 0.8. Within the range of 5 to 1.5, the number of lower twists and the number of upper twists may be made different.

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

  Further, in this embodiment, the topping rubber of the carcass ply 6A is made of rubber having higher elasticity than that of the conventional one, specifically, rubber having a complex elastic modulus E * t of 5 to 13 MPa. Yes. By adopting rubber having high elasticity as the topping rubber of the carcass cord in this manner, distortion applied to the carcass cord 20 when the tire is deformed can be reduced, and further improvement in run-flat durability can be achieved. Note that if the complex elastic modulus E * t is less than 5 MPa, the above effect cannot be sufficiently expected. Conversely, if the complex elastic modulus E * t exceeds 13 MPa, the rubber becomes too hard and the ride comfort may be deteriorated at a stretch. From such a viewpoint, the lower limit value of the complex elastic modulus E * t is preferably 5.5 MPa or more, more preferably 6 MPa or more, and the upper limit value is preferably 11 MPa or less, more preferably 9 MPa or less.

  Further, in the run flat tire 1 of the present invention, the insulation rubber 11 is disposed in a region between the carcass 6 and the belt layer 7. Such an insulation rubber 11 enhances the compression resistance of the tread portion 2 and, for example, as shown in FIG. 3, the amount of deflection Lf of the tread portion 2 in the tire radial direction is higher than that of the conventional (FIG. 9). And can be kept small. Such an action is more effectively exhibited in combination with the carcass cord of the aramid fiber having a limited twist coefficient T. Further, along with this, the contact width TCW of the tread shoulder portion can be increased to suppress a significant increase in the contact pressure there. The reason why the insulation rubber 11 is disposed in the region between the carcass 6 and the belt layer 7 is that even if the rubber layer is disposed in this region, the influence on the steering stability is relatively small.

  The insulation rubber 11 includes a crown rubber portion 12 disposed in the center portion of the tread and a pair of shoulder rubber portions 13 disposed on both outer sides in the tire axial direction and having a different composition from the crown rubber portion 12. 13. The insulation rubber 11 of the present embodiment is formed continuously in the tire axial direction at the tread portion 2 by connecting the crown rubber portion 12 and the shoulder rubber portion 13.

  The crown rubber portion 12 is made of rubber having a hardness Hdc of at least 70 degrees, preferably 75 degrees or more, and more preferably 80 degrees or more, in order to suppress the bending of the tread central portion. desirable. When the hardness Hdc is less than 70 degrees, the compression resistance at the center of the tread cannot be sufficiently increased, and as a result, the amount of bending inward in the tire radial direction cannot be suppressed. On the other hand, if the hardness Hdc of the crown rubber portion 12 is too large, the ride comfort during normal running is deteriorated, and a significant hardness difference from the topping rubber of the carcass ply 6A and / or the belt plies 7A and 7B occurs. There is a problem that causes stress concentration and lowering of adhesive strength. From such a viewpoint, the hardness Hdc of the crown rubber portion is 99 degrees or less, preferably 90 degrees or less, and more preferably 85 degrees or less.

  Further, the loss tangent tan δ of the crown rubber portion 12 is not particularly limited. However, if the loss tangent tan δ is too large, the durability is likely to deteriorate due to heat generation. From this viewpoint, the loss tangent tan δ is preferably 0.25 or less, more preferably 0.20 or less. On the other hand, the lower limit of the loss tangent tan δ is not particularly limited, but if it is too small, it tends to be difficult to maintain the rubber hardness. From such a viewpoint, the loss tangent tan δ of the crown rubber portion 12 is preferably 0.10 or more, and more preferably 0.15 or more.

  Further, the tread shoulder portion that repeats grounding and separation from the road surface during run-flat traveling is subjected to very large distortion compared to the tread center portion. For this reason, in the shoulder rubber portion 13 of the insulation rubber 11 disposed on the tread shoulder portion, a rubber having a low heat generation property than the crown rubber portion 12, that is, a rubber having a loss tangent tan δ smaller than that of the crown rubber portion 12. Used.

  Although the specific value of the loss tangent tan δ of the shoulder rubber portion 13 is not particularly limited, it is preferably 0.12 or less, more preferably 0.10 or less, and further preferably 0.09 or less. As described above, when the loss tangent tan δ of the shoulder rubber portion 13 is specifically limited, heat generation at the tread shoulder portion during the run-flat running can be more reliably suppressed, and the durability can be further improved. On the other hand, if the loss tangent tan δ of the shoulder rubber portion 13 is too small, sufficient rubber hardness tends not to be obtained, so 0.04 or more, more preferably 0.06 or more is desirable.

  Further, the hardness Hds of the shoulder rubber portion 13 is not particularly limited. However, if the hardness Hds is too small, the strain between the belt layer 7 and the carcass 6 is increased, and the steering stability may be deteriorated. From such a viewpoint, the hardness Hds of the shoulder rubber portion 13 is preferably 50 degrees or more, more preferably 55 degrees or more. On the other hand, if the hardness Hds of the shoulder rubber portion 13 is too large, the loss tangent tan δ tends to increase accordingly, and the riding comfort during normal traveling tends to deteriorate. From such a viewpoint, the hardness Hds is preferably less than 70 degrees, more preferably 65 degrees or less.

  In order to further improve the run-flat durability and ride comfort in a well-balanced manner, the difference (Hdc−Hds) between the hardness Hdc of the crown rubber portion 12 and the hardness Hds of the shoulder rubber portion 13 is preferably 10 degrees or more. The upper limit is preferably 15 degrees or more, and the upper limit is preferably 25 degrees or less, more preferably 20 degrees or less.

  Further, as shown in FIG. 2, the width RW in the tire axial direction of the insulation rubber 11 is desirably 90 to 110% of the width BWo in the tire axial direction of the belt ply 7B disposed on the outermost side in the tire radial direction. . When the width RW of the insulation rubber 11 is less than 90% of the width BWo of the belt ply 7B, the shoulder rubber portion 13 cannot be arranged in a wide range on the tread shoulder portion, and as a result, a heat generation suppressing effect is sufficiently obtained. There is a risk of not being able to. On the contrary, when the width RW of the insulation rubber 11 exceeds 110% of the width BWo of the belt ply 7B, the heat generation suppressing effect cannot be expected for the molding process becoming difficult. Note that the performance of the belt layer 7 is usually greatly contributed by the overlapping portions of the belt plies 7A and 7B. Further, in a general tire, a belt ply having a small width is disposed on the outermost side in the tire radial direction. In this embodiment, the width RW of the insulation rubber 11 is equal to the width BWo of the outer belt ply 7B. Associated.

  In the insulation rubber 11, the width CW of the crown rubber portion 12 in the tire axial direction is preferably 60% or more, more preferably 65% or more of the width BWo of the belt ply 7B. When the width CW of the crown rubber portion 12 is less than 60% of the width BWo of the belt ply 7B, the effect of suppressing the bending of the tread central portion tends to be reduced. On the other hand, even if the width CW of the crown rubber portion 12 is too large, the region of the shoulder rubber portion 13 becomes small, and the heat generation suppressing effect of the tread shoulder portion tends to be reduced. From such a viewpoint, the width CW of the crown rubber portion 12 is desirably 80% or less, more preferably 75% or less, of the width BWo of the belt ply 7B. In the present embodiment, the crown rubber portion 12 is arranged with its width center substantially aligned with the tire equator C. The shoulder rubber portion 13 is also provided symmetrically with respect to the tire equator C.

  The thickness ti of the insulation rubber 11 is preferably 2.0 mm or more, more preferably 2.5 mm or more, and further preferably 3.0 mm or more. Here, the thickness of the insulation rubber 11 is measured as the distance between cords between the carcass ply 6A and the innermost belt ply 7A at the position of the tire equator C for convenience. When the thickness ti of the insulation rubber 11 is less than 2.0 mm, there is a possibility that sufficient compression resistance cannot be given particularly in the center portion of the tread. On the other hand, if the thickness ti of the insulation rubber 11 is too large, the exothermic property and the steering stability may be deteriorated. From such a viewpoint, the thickness ti of the insulation rubber 11 is preferably 10.0 mm or less, more preferably 8.0 mm or less, and still more preferably 6.0 mm or less.

  Note that the thickness ti of the insulation rubber 11 may be constant or may vary in the width direction of the tread. In the present embodiment, a mode in which at least the belt layer 7 and the carcass 6 extend with a substantially constant thickness ti is shown.

  In addition, as shown in FIG. 5, the insulation rubber 11 can be blended with, for example, the short fiber f in the crown rubber portion 12 or the like. In the present embodiment, the short fibers f are oriented in the longitudinal direction along the width direction of the insulation rubber 11. Such a crown rubber portion 12 is preferable in that the compression resistance in the width direction Y can be further enhanced without a substantial increase in mass. The short fibers f are preferably organic fibers such as nylon, polyester, aramid, rayon, vinylon, aromatic polyamide, cotton, cellulose resin, or crystalline polybutadiene. The short fibers f are preferably those having an average fiber diameter of about 1 to 100 μm and an average fiber length of about 0.1 to 5 mm, for example, in order to improve adhesion to rubber.

  FIG. 6 shows still another embodiment of the insulation rubber 11. In this embodiment, a mode in which the thickness ti of the insulation rubber 11 gradually increases from the tire equator C toward the outer side in the tire axial direction is shown. Such an insulation rubber 11 can preferably absorb a difference in curvature between the belt ply 7A and the carcass ply 6A in the tire cross section, and the shoulder rubber portion 13 having a relatively large thickness generates more heat at the tread shoulder portion. It is preferable in that it is further suppressed.

Furthermore, the run-flat tire 1 of the present embodiment has a tire outer surface profile (contour line) TL as shown in FIG. 7 (regular unloaded state). The profile TL is specified in a state where the groove of the tread portion 2 is filled. 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 is gradually decreased 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 provided with the profile can significantly reduce the weight of the tire. Therefore, even when the insulation rubber 11 is provided, 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 decreased continuously as in the present embodiment, but can be decreased step by step. Furthermore, since the profile TL reduces the vertical spring of the tire, the riding comfort during normal driving is excellent.

  The present invention is particularly suitable for a passenger car, but it is needless to say that the present invention is not limited to the illustrated embodiment and can be implemented in various forms.

  In order to confirm the effect of the present invention, a plurality of types of run-flat tires (Examples) according to the present invention having a tire size of “245 / 40R18” based on the specifications of Table 2 were prototyped and the following performances were tested. For comparison, tests were also performed on run-flat tires having no insulation rubber (Comparative Examples 1 to 4) and tires having an insulation rubber composed of one kind (Comparative Examples 5 and 6). It was broken.

Further, the following two types A and B of the tire outer surface profile were tested.
A: RY60 = 0.06, RY75 = 0.08, RY90 = 0.19, RY100 = 0.57
B: RY60 = 0.09, RY75 = 0.14, RY90 = 0.37, RY100 = 0.57
The common specifications of the side reinforcing rubber layer are as follows.

<Common specifications for side reinforcing rubber layer>
Tire axial length Wo that overlaps with the belt layer Wo: 15mm
Tire radial length Wi which overlaps with bead apex rubber Wi: 10mm
Tire radial length L: 30mm
Maximum thickness tc: 7mm
Table 1 shows two typical blends used in the crown rubber portion and the shoulder rubber portion.

  Further, the test method is as follows.

<Runflat durability>
Each test tire was assembled on the rim described below, filled with an internal pressure of 230 kPa, and allowed to stand at a temperature of 38 ± 2 ° C. for 34 hours, and then the valve core of the rim was removed to allow the tire lumen to communicate freely with the atmosphere. And in this state, it was made to run on the drum test machine which has a drum with a radius of 1.7 m on the following conditions, and the running distance until a tire broke was measured. The results were expressed as an index with Comparative Example 1 as 100. The larger the value, the better.
Rims: 18 x 8.5J
Speed: 80km / h
Longitudinal load: 4.14kN

<Tire mass>
The mass of each test tire was measured. The results are shown as an index with Comparative Example 1 as 100. A smaller number indicates a lighter weight.

<Vertical spring coefficient>
A test tire mounted on a rim (18 × 8.5 J) was grounded on a flat surface under conditions of an internal pressure of 230 kPa and a load of 5 kPa, and the amount of vertical deflection of the tire was measured. Then, the vertical spring constant was approximately obtained by dividing the load 5 kN by the vertical deflection amount. 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 and handling stability>
Attaching four test tires to a 4300cc domestic FR vehicle, and driving responsiveness and grip feeling on a dry asphalt road surface with the above rim and internal pressure of 230 kPa, depending on the driver's sensuality evaluated. Similarly, on asphalt step roads, Belgian roads (cobblestone roads), and Bitzmann roads (roads covered with pebbles), sensory evaluations related to riding comfort such as ruggedness, push-up and damping were performed. In each case, the evaluation was made with a score of Comparative Example 1 as 100 points. The larger the value, the better.
Table 2 shows the test results.

  As a result of the test, it was confirmed that the tires of the examples improved the run-flat durability without increasing the tire mass as compared with the comparative examples. In addition, no substantial difference was found in ride comfort and handling stability as compared with the comparative example.

It is sectional drawing of the run flat tire which shows embodiment of this invention. It is the elements on larger scale which expanded the tread part. It is sectional drawing of the tire which shows the run flat state of FIG. It is a diagram for explaining twist of a carcass cord. It is a perspective view which shows other embodiment of an insulation rubber. It is a partial expanded sectional view of the tread part which shows other embodiment of an insulation rubber. 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. It is sectional drawing of the run flat state of the conventional run flat tire.

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 7B Outermost belt ply 9 Side reinforcement rubber layer 11 Insulation rubber 12 Crown rubber part 13 Shoulder rubber part

Claims (8)

A carcass extending from the tread portion through the sidewall portion to the bead core of the bead portion, a belt layer disposed inside the tread portion and radially outward of the carcass, and a cross section disposed inside the carcass of the sidewall portion A run-flat tire having a substantially crescent-shaped side reinforcing rubber layer,
The carcass is composed of a carcass ply in which a carcass cord arranged at an angle of 45 to 90 ° with respect to the tire equator is covered with a topping rubber, and the carcass cord has a twist coefficient T expressed by the following formula (1) of 0. It is composed of aramid fibers that are 5 to 0.7, and between the carcass and the belt layer, there is an insulation rubber extending in the tire axial direction,
The insulation rubber includes at least a crown rubber portion disposed in a tread center portion and a pair of shoulder rubber portions disposed on both outer sides in the tire axial direction and having a different composition from the crown rubber portion,
The crown hardness by durometer type A based on JIS-K6253 was measured at a temperature 23 ° C. of the rubber portion is 70 to 99 degrees, and the hardness and a loss tangent tanδ of the shoulder rubber portion of the crown rubber portion run-flat tire, wherein the less than hardness and a loss tangent tan [delta.
T = N × √ {(0.125 × D / 2) / ρ} × 10 ⁻³ (1)
However, N is the number of twists (times / 10 cm), D is the total display decitex (fineness) of the cord, and ρ is the specific gravity of the cord material.
The loss tangent tan of the crown rubber portion is 0.15 to 0.25, and wherein the hardness Moreover the loss tangent tanδ less than 50 degrees and 70 degrees of shoulder rubber portion is 0.04 to 0.12 The run flat tire according to claim 1.
  The belt layer is composed of a plurality of belt plies stacked in the tire radial direction, and the width of the insulation rubber in the tire axial direction is the tire axial direction of the belt ply disposed on the outermost side in the tire radial direction. The run flat tire according to claim 1 or 2, which is 90 to 110% of the width of the tire.   The belt layer is composed of a plurality of belt plies stacked in the tire radial direction, and the width of the crown rubber portion in the tire axial direction is the tire axial direction of the belt ply disposed on the outermost side in the tire radial direction. The run flat tire according to any one of claims 1 to 3, wherein the run flat tire is 60 to 85% of the width of the tire.   The run flat tire according to any one of claims 1 to 4, wherein the insulation rubber has a thickness of 2.0 to 10.0 mm.   The run-flat tire according to any one of claims 1 to 5, wherein the twist coefficient T of the carcass cord is 0.6 to 0.7.   The pneumatic tire according to any one of claims 1 to 6, wherein the topping rubber of the carcass ply has a complex elastic modulus E * t of 5 to 13 MPa. 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). The run flat according to any one of claims 1 to 7, wherein a radius of curvature (RC) of a tire outer surface gradually decreases and satisfies the following relationship in a section from the intersection (CP) to the point (P). tire.
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.)