JP6274500B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire. Specifically, the present invention relates to a run flat tire provided with a load support layer.

  In recent years, run-flat tires having a load support layer inside a sidewall have been developed and are becoming popular. For this support layer, a highly hard crosslinked rubber is used. This run flat tire is called a side reinforcement type. In this type of run flat tire, when the internal pressure is reduced by puncture, the load is supported by the support layer. This support layer suppresses the bending of the tire in the puncture state. Even if traveling is continued in a punctured state, the hardened crosslinked rubber suppresses heat generation in the support layer. This run-flat tire can travel a certain distance even in a punctured state. Automobiles equipped with this run-flat tire need not have spare tires. By adopting this run flat tire, tire replacement at an inconvenient place can be avoided.

  When the run of the run flat tire in the punctured state is continued, the deformation and restoration of the support layer are repeated. By repeating this, heat is generated in the support layer, and the tire reaches a high temperature. This heat causes breakage of the rubber member constituting the tire and peeling between the rubber members. Running with a tire that has been damaged and peeled is impossible. A run flat tire capable of running for a long time in a puncture state is desired.

  The durability of the run-flat tire when traveling in a puncture state (referred to as run-flat durability) can be increased by increasing the support layer. However, a large support layer increases the tire mass and rolling resistance. This deteriorates the fuel consumption performance of the tire. Furthermore, the longitudinal spring constant of the tire is increased by increasing the support layer. This causes a deterioration in ride comfort. Examples of study of run-flat tires having a support layer are disclosed in Japanese Unexamined Patent Application Publication Nos. 2009-126409 and 2007-153120.

JP 2009-126409 A JP 2007-153120 A

  In the tires of Japanese Patent Application Laid-Open Nos. 2009-126409 and 2007-153120, durability in puncture traveling is adjusted by adjusting the width of the support layer and the tire in a portion from the tread to the sidewall (referred to as a buttress portion). Improves sex. However, the buttress portion of these tires is larger than that of conventional tires. In these tires, increases in tire mass and longitudinal spring constant are not sufficiently suppressed.

  As a result of confirming in detail the running state during puncture of the conventional run-flat tire, the inventors have found that not only the buttress portion but also the bead portion are greatly deformed during running in the puncture state. And when the buttress part was enlarged and the deformation | transformation was suppressed, the deformation | transformation of a bead part will become large and it discovered that it became easy to occur that a bead part destroys. In the tires of Japanese Patent Application Laid-Open Nos. 2009-126409 and 2007-153120, the destruction of the bead portion has not been studied. In these tires, the durability may be lowered due to the destruction of the bead portion.

  An object of the present invention is to provide a pneumatic tire having improved durability in a puncture state and having reduced mass, rolling resistance and longitudinal spring constant.

  The pneumatic tire according to the present invention has a tread whose outer surface forms a tread surface, a pair of sidewalls that extend substantially inward in the radial direction from the end of the tread, and each of which is substantially radially inward of the sidewalls. A pair of clinch positioned, a pair of beads positioned axially inward of the clinch, and a carcass bridged between one bead and the other bead along the inside of the tread and the sidewall And a pair of load support layers that are positioned on the inner side in the axial direction than the sidewalls. The loss tangent LT of the load support layer is not less than 0.06 and not more than 0.08. In a cross section perpendicular to the circumferential direction, the distance measured along the axial inner surface of the load layer from the radially outer end to the inner end of the load support layer is L0, and the axial inner surface of the load support layer The point located above and the distance from the radially outer end of the load support layer is (L0 / 3) is P1, and when this tire is incorporated in the rim, the contact between the clinch and the flange of the rim When the point of the outer end of the portion is P2, the ratio (T1 / T2) of the thickness T1 from the outer surface to the inner surface of the tire at the point P1 to the thickness T2 from the outer surface to the inner surface of the tire at the point P2 is 0.8 or more and 1.1 or less.

Preferably, the complex elastic modulus E ^* of the load support layer is 9 MPa or more and 11 MPa or less.

  Preferably, the bead includes a core and an apex extending radially outward from the core, and when the point where the tire has the maximum width on the outer surface of the sidewall is Pw, the radius In the direction, the ratio (BH / H) of the height BH from the base line to the outer end of the apex to the height H from the base line to the point Pw is 0.9 or more and 1.0 or less.

  Preferably, the tire has a large number of dimples on a side surface which is a region that can be viewed from the axial direction on the outer surface of the tire.

  The pneumatic tire according to the present invention includes a pair of load support layers positioned on the inner side in the axial direction of the carcass. The loss tangent LT of this support layer is 0.06 or more and 0.08 or less, and the loss tangent of this support layer is smaller than the conventional one. When running in a puncture state, the heat generated by this support layer is small. In the tire having this support layer, damage and peeling of the rubber member are suppressed. This tire has high durability.

  Furthermore, the support layer with a small calorific value can be made thinner than the conventional support layer. In the present tire, the thickness of the buttress portion provided with the support layer is substantially equal to or less than the thickness of the bead portion. In this tire, the mass, rolling resistance, and longitudinal spring constant are reduced as compared with the conventional run flat tire. Further, in the present tire, by reducing the thickness of the buttress portion, a large deformation of the bead portion is suppressed as compared with the conventional run flat tire. In this tire, a decrease in durability due to the bead portion is suppressed. According to the present invention, a pneumatic tire with improved run flat durability and reduced mass, rolling resistance, and longitudinal spring constant can be obtained.

FIG. 1 is a cross-sectional view showing a part of a tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the tire of FIG. FIG. 3 is a cross-sectional view showing a part of a tire according to another embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view showing a part of the tire of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 shows a pneumatic tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In FIG. 1, an alternate long and short dash line CL represents the equator plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 2 includes a tread 4, a wing 6, a sidewall 8, a clinch 10, a bead 12, a carcass 14, a belt 16, a band 18, an inner liner 20, a chafer 22, and a load support layer 24. The tire 2 is a tubeless type. The tire 2 is mounted on a passenger car.

  The tread 4 has a shape protruding outward in the radial direction. The tread 4 forms a tread surface 26 that contacts the road surface. A groove 32 is carved in the tread surface 26. The groove 32 forms a tread pattern. The tread 4 has a base layer 28 and a cap layer 30. The cap layer 30 is located on the radially outer side of the base layer 28. The cap layer 30 is laminated on the base layer 28. The base layer 28 is made of a crosslinked rubber having excellent adhesiveness. A typical base rubber of the base layer 28 is natural rubber. The cap layer 30 is made of a crosslinked rubber having excellent wear resistance, heat resistance, and grip properties.

  The wing 6 is located between the tread 4 and the sidewall 8. The wing 6 is joined to each of the tread 4 and the sidewall 8. The wing 6 is made of a crosslinked rubber having excellent adhesiveness.

  The sidewall 8 extends substantially inward in the radial direction from the end of the tread 4. The radially outer end of the sidewall 8 is joined to the tread 4 and the wing 6. The radially inner end of the sidewall 8 is joined to the clinch 10. The sidewall 8 is made of a crosslinked rubber having excellent cut resistance and weather resistance. The sidewall 8 is located outside the carcass 14 in the axial direction. The sidewall 8 prevents the carcass 14 from being damaged.

  From the viewpoint of preventing damage, the hardness of the sidewall 8 is preferably 50 or more, and more preferably 55 or more. From the viewpoint of riding comfort in a normal state, the hardness is preferably 70 or less, and more preferably 65 or less. In the present application, the hardness is measured with a type A durometer in accordance with the provisions of “JIS K6253”. This durometer is pressed against the cross section shown in FIG. 1, and the hardness is measured. The measurement is made at a temperature of 23 ° C. The hardness of the clinch 10, the apex, and the load support layer 24 to be described later is also measured in the same manner.

  The clinch 10 is located substantially inside the sidewall 8 in the radial direction. The clinch 10 is located outside the beads 12 and the carcass 14 in the axial direction. The clinch 10 is made of a crosslinked rubber having excellent wear resistance. The clinch 10 contacts the rim flange.

  From the viewpoint of wear resistance, the hardness of the clinch 10 is preferably 60 or more, and more preferably 65 or more. In light of riding comfort in a normal state, the hardness is preferably 90 or less, and more preferably 80 or less.

  The bead 12 is located radially inward of the sidewall 8. The bead 12 is located on the inner side in the axial direction than the clinch 10. The bead 12 includes a core 34 and an apex 36 that extends radially outward from the core 34. The core 34 is ring-shaped and includes a wound non-stretchable wire. A typical material for the wire is steel. The apex 36 is tapered outward in the radial direction. The apex 36 is made of a highly hard crosslinked rubber.

  From the viewpoint of preventing deformation of the bead 12 parts, the hardness of the apex 36 is preferably 60 or more, and more preferably 65 or more. In light of riding comfort in a normal state, the hardness is preferably 90 or less, and more preferably 80 or less.

  The carcass 14 includes a carcass ply 14a. The carcass ply 14a is bridged between the beads 12 on both sides. The carcass ply 14 a is along the tread 4 and the sidewall 8. The carcass ply 14a is folded around the core 34 from the inner side to the outer side in the axial direction. By this folding, a main portion 38 and a folding portion 40 are formed in the carcass ply 14a. The end of the folded portion 40 reaches just below the belt 16. In other words, the folded portion 40 overlaps the belt 16. The carcass 14 has a so-called “super high turn-up structure”. The carcass 14 having an ultra high turn-up structure contributes to the durability of the tire 2 in a punctured state. The carcass 14 contributes to durability in the puncture state.

  A portion of the carcass 14 that overlaps the load support layer 24 is separated from the inner liner 20. In other words, the carcass 14 is curved due to the presence of the load support layer 24.

  Although not shown, the carcass ply 14a includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is 75 ° to 90 °. In other words, the carcass 14 has a radial structure. The cord is made of organic fiber. Preferred organic fibers include polyethylene terephthalate fiber, nylon fiber, rayon fiber, polyethylene naphthalate fiber and aramid fiber.

  The belt 16 is located inside the tread 4 in the radial direction. The belt 16 is laminated with the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 includes an inner layer 16a and an outer layer 16b. As apparent from FIG. 2, the width of the inner layer 16a is slightly larger than the width of the outer layer 16b. Although not shown, each of the inner layer 16a and the outer layer 16b is composed of a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is usually 10 ° to 35 °. The inclination direction of the cord of the inner layer 16a with respect to the equator plane is opposite to the inclination direction of the cord of the outer layer 16b with respect to the equator plane. A preferred material for the cord is steel. An organic fiber may be used for the cord. The belt 16 may include three or more layers.

  The band 18 is located on the radially outer side of the belt 16. In the axial direction, the width of the band 18 is substantially equal to the width of the belt 16. Although not shown, the band 18 is composed of a cord and a topping rubber. The cord is wound in a spiral. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is 5 ° or less, and further 2 ° or less. Since the belt 16 is restrained by this cord, lifting of the belt 16 is suppressed. The cord is made of organic fiber. Examples of preferable organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 16 and the band 18 constitute a reinforcing layer. The reinforcing layer may be formed only from the belt 16. A reinforcing layer may be formed only from the band 18.

  The inner liner 20 is bonded to the inner surfaces of the carcass 14 and the load support layer 24. The inner liner 20 is made of a crosslinked rubber. The inner liner 20 is made of rubber having excellent air shielding properties. The inner liner 20 holds the internal pressure of the tire 2.

  The chafer 22 is located in the vicinity of the bead 12. When the tire 2 is incorporated into the rim, the chafer 22 comes into contact with the rim. By this contact, the vicinity of the bead 12 is protected. In this embodiment, the chafer 22 is made of a cloth and a rubber impregnated in the cloth. The chafer 22 may be integrated with the clinch 10. In this case, the material of the chafer 22 is the same as that of the clinch 10.

  The load support layer 24 is located on the inner side in the axial direction of the sidewall 8. The support layer 24 is located on the inner side in the axial direction than the carcass 14. The support layer 24 is sandwiched between the carcass 14 and the inner liner 20. The support layer 24 tapers inward and outward in the radial direction. This support layer 24 has a similar shape to the crescent moon. The support layer 24 is made of a highly hard crosslinked rubber. When the tire 2 is punctured, the support layer 24 supports the load. Since the support layer 24 is a rubber lump, it can sufficiently withstand the compressive load. The support layer 24 allows the tire 2 to travel a certain distance even in a puncture state. The tire 2 is also called a run flat tire. The tire 2 is a side reinforcing type.

  In the radial direction, the inner end 42 of the support layer 24 is located inside the outer end 44 of the apex 36. In other words, the support layer 24 overlaps the apex 36. Typically, the radial distance between the inner end 42 of the support layer 24 and the outer end 44 of the apex 36 is 5 mm or more and 50 mm or less, and further 10 mm or more and 40 mm or less. In the tire 2 in which this distance is within this range, a uniform rigidity distribution can be obtained. This distance may not be in this range.

  The radially outer end 46 of the support layer 24 is located on the inner side in the axial direction than the end 48 of the belt 16. In other words, the support layer 24 overlaps the belt 16. Typically, the axial distance between the outer end 46 of the support layer 24 and the end 48 of the belt 16 is 2 mm or more and 50 mm or less, and further 5 mm or more and 40 mm or less. In the tire 2 in which this distance is within this range, a uniform rigidity distribution can be obtained. This distance may not be in this range.

  In the tire 2, unless otherwise specified, the dimensions and angles of the members of the tire 2 are measured in a state where the tire 2 is incorporated in a normal rim and the tire 2 is filled with air so as to have a normal internal pressure. . At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures. In addition, when the tire 2 is for passenger cars, dimensions and angles are measured in a state where the internal pressure is 180 kPa.

  In FIG. 2, a double-headed arrow L <b> 0 is a distance measured along the axial inner side surface of the support layer 24 from the radially outer end 46 to the inner end 42 of the support layer 24 in a cross section perpendicular to the circumferential direction. The point P1 is located on the inner side surface in the axial direction of the support layer 24, and the distance from the radially outer end 46 of the support layer 24 is (L0 / 3). In FIG. 2, a double-headed arrow T1 is the thickness from the outer surface to the inner surface of the tire 2 at the point P1. More specifically, the thickness T1 is a distance from the outer surface of the sidewall 8 to the inner surface of the inner liner 20 measured along the normal line drawn from the point P1. The thickness T1 is a representative value of the thickness of the buttress portion.

  In FIG. 2, a point P2 indicates a radially outer end of a contact portion between the clinch 10 and the rim flange in a state where the tire 2 is assembled with a normal rim and the tire 2 is filled with air so as to have a normal internal pressure. It is. A double-headed arrow T2 is the thickness from the outer surface to the inner surface of the tire 2 at the point P2. More specifically, the thickness T2 is a distance from the outer surface of the clinch 10 to the inner surface of the inner liner 20 measured along the normal line drawn from the point P2. The thickness T2 is a representative value of the thickness of 12 parts of the bead.

  In the tire 2, the ratio (T1 / T2) of the thickness T1 to the thickness T2 is 0.8 or more and 1.1 or less. In other words, in the tire 2, the thickness of the buttress portion is substantially equal to or less than the thickness of the bead 12 portion. The thickness of the buttress portion is made thinner than the thickness of the buttress portion of the conventional run flat tire.

  In the tire 2, the loss tangent LT of the support layer 24 is not less than 0.06 and not more than 0.08. The loss tangent of the support layer 24 is smaller than the conventional one. In other words, the support layer 24 generates a smaller amount of heat when it is repeatedly deformed and restored as compared with a conventional run-flat tire.

In the present invention, the loss tangent LT and the complex elastic modulus E ^{*, which} will be described later, are described below using a viscoelastic spectrometer (“VESF-3” manufactured by Iwamoto Seisakusho) in accordance with the provisions of “JIS K 6394”. Measured under the conditions shown in.
Initial strain: 10%
Amplitude: ± 2.0%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 100 ° C

  Below, the effect of this invention is demonstrated.

  In a run flat tire provided with a load support layer, this support layer supports the load when the tire is punctured. When the run of the flat tire in the punctured state is continued, heat is generated in the support layer, and the tire reaches a high temperature. This heat causes breakage of the rubber member constituting the tire and peeling between the rubber members. Run-flat durability can be increased by increasing the support layer. However, a large support layer increases the mass of the tire, the rolling resistance of the tire, and the longitudinal spring constant of the tire. Further, if the support layer is enlarged to suppress the deformation of the buttress portion, the deformation of the bead portion increases, and the bead portion may be destroyed.

  As described above, in the present tire 2, the loss tangent LT of the load support layer 24 is 0.06 or more and 0.08 or less, which is smaller than the conventional one. For this reason, when the vehicle travels in a puncture state, the heat generation amount of the support layer 24 is small. In the tire 2 having the support layer 24, damage and peeling of the rubber member are suppressed. The tire 2 has a high run-flat durability.

  The loss tangent LT of the support layer 24 is more preferably 0.075 or less. In the tire having the support layer 24 having a loss tangent LT of 0.075 or less, the rolling resistance can be effectively reduced. The loss tangent LT is preferably 0.065 or more. In the support layer 24 having a loss tangent LT of 0.065 or more, a decrease in durability due to an excessive decrease in loss tangent is suppressed.

  The support layer 24 that generates a small amount of heat can be made thinner than the conventional support layer 24. As described above, in the tire 2, the ratio (T1 / T2) is 0.8 or more and 1.1 or less. In other words, the thickness of the buttress portion of the tire 2 is substantially equal to or less than the thickness of the bead 12 portion. In the tire 2, the mass, rolling resistance, and longitudinal spring constant are reduced as compared with the conventional run-flat tire. Further, in the present tire 2, the deformation of the bead 12 part is suppressed by reducing the thickness of the buttress part as compared with the conventional run flat tire. Thereby, the fall of durability by destruction of 12 parts of beads is controlled. According to the present invention, a pneumatic tire 2 with improved run flat durability and reduced mass, rolling resistance, and longitudinal spring constant compared to a conventional run flat tire can be obtained.

  The ratio (T1 / T2) is preferably 1.0 or less. In the tire 2 having a ratio (T1 / T2) of 1.0 or less, the mass, the rolling resistance, and the longitudinal spring constant are further reduced, and further, excessive deformation of the bead 12 part is suppressed in a punctured state. This bead 12 part has sufficient durability. The ratio (T1 / T2) is preferably 0.9 or more. In the tire 2 having the ratio (T1 / T2) of 0.9 or more, the buttress portion has sufficient durability in the puncture state.

  In the tire 2, the thickness T1 is preferably 10.0 mm or less. In the tire 2 having a thickness T1 of 10.0 mm or less, the mass, rolling resistance, and longitudinal spring constant are reduced, and excessive deformation of the bead 12 portion is suppressed in a punctured state. This bead 12 part has sufficient durability. In this respect, the thickness T1 is more preferably 9.5 mm or less. The thickness T1 is preferably 8.0 mm or more. In the tire 2 having a thickness T1 of 8.0 mm or more, the buttress portion has sufficient durability. In this respect, the thickness T1 is more preferably 8.5 mm or more.

  In FIG. 2, a double arrow M is the maximum thickness of the support layer 24. Specifically, the thickness M is the maximum value among the thicknesses of the support layer 24 measured along a normal drawn from a point on the inner side surface in the axial direction of the support layer 24. In the tire 2, the thickness M is preferably 9.0 mm. In the tire 2 having a thickness M of 9.0 mm or less, the mass, rolling resistance, and longitudinal spring constant are reduced, and excessive deformation of the bead 12 part is suppressed in a punctured state. This bead 12 part has sufficient durability. The thickness M is preferably 7.0 mm or more. In the tire 2 having a thickness M of 7.0 mm or more, the buttress portion has sufficient durability.

The complex elastic modulus E ^* of the support layer 24 is preferably 9 MPa or more. The support layer 24 having a complex elastic modulus E ^* of 9 MPa or more suppresses vertical bending in a punctured state. In the tire 2, good steering stability in a punctured state can be realized. Moreover, this tire has sufficient run-flat durability. In this respect, the complex elastic modulus E ^* is more preferably 9.5 MPa or more. The complex elastic modulus E ^* of the support layer 24 is preferably 11 MPa or less. The support layer 24 having a complex elastic modulus E ^* of 11 MPa or less has a reduced longitudinal spring constant. The tire 2 can achieve a good ride comfort. In this respect, the complex elastic modulus E ^* is more preferably 10.5 MPa or less.

  The hardness H of the support layer 24 is preferably 60 or more. The support layer 24 having a hardness H of 60 or more suppresses vertical deflection in the puncture state. In the tire 2, good steering stability in a punctured state can be realized. In this respect, the hardness H is more preferably equal to or greater than 65. The hardness H of the support layer 24 is preferably 90 or less. The support layer 24 having a hardness H of 90 or less has a reduced longitudinal spring constant. The tire 2 can achieve a good ride comfort. In this respect, the hardness H is more preferably equal to or less than 80.

  In FIG. 2, reference symbol Pw is a point where the width of the tire 2 is maximized on the outer surface of the sidewall 8. A double arrow H is a height in the radial direction from the base line BL to the point Pw. A double arrow BH is a height from the base line BL to the radially outer end 44 of the apex 36. The ratio (BH / H) is preferably 0.9 or more. In the tire 2 having a ratio (BH / H) of 0.9 or more, the 12 parts of the bead have sufficient durability in running during puncture. The ratio (BH / H) is preferably 1.0 or less. In the tire 2 having a ratio (BH / H) of 1.0 or less, the mass and the longitudinal spring constant can be reduced.

  FIG. 3 shows a pneumatic tire 50 according to another embodiment of the present invention. In FIG. 3, the vertical direction is the radial direction of the tire 50, the horizontal direction is the axial direction of the tire 50, and the direction perpendicular to the paper surface is the circumferential direction of the tire 50. In FIG. 3, an alternate long and short dash line CL represents the equator plane of the tire 50. The shape of the tire 50 is symmetrical with respect to the equator plane except for the tread pattern.

  The tire 50 includes a tread 52, a wing 54, a sidewall 56, a clinch 58, a bead 60, a carcass 62, a belt 64, a band 66, an inner liner 68, a chafer 70, and a load support layer 72. The tire 50 is a tubeless type. The tire 50 is attached to a passenger car.

  As shown in FIG. 3, the tire 50 includes a large number of dimples 74 on its side surface. In the present invention, the side surface means a region of the outer surface of the tire 50 that can be viewed from the axial direction. Typically, the dimple 74 is formed on the surface of the sidewall 56. A portion of the side surface other than the dimple 74 is a land 76. In FIG. 3, what is indicated by a double-pointed arrow De is the depth of the dimple 74.

  FIG. 4 is an enlarged front view showing a part of the sidewall 56 of the tire 50 of FIG. In FIG. 4, the left-right direction is the circumferential direction, and the up-down direction is the radial direction. FIG. 4 shows a large number of dimples 74. The outline of each dimple 74 is a rectangle. In other words, in the dimple 74, the circumferential length D1 is larger than the radial length D2. The outline of the dimple 74 may be an ellipse. The contour of the dimple 74 may have other shapes. Similar dimples 74 may be formed on the clinch 58.

  The tire 50 has the same structure as the tire 2 of FIG. 1 except that the dimple 74 is provided on the side surface.

  Below, the effect of this invention is demonstrated.

  Similar to the tire 2 in FIG. 1, in the present tire 50, the loss tangent LT of the load support layer 72 is 0.06 or more and 0.08 or less, which is smaller than the conventional one. For this reason, when the vehicle travels in a puncture state, the heat generation amount of the support layer 72 is small. In the tire 50 having the support layer 72, damage and peeling of the rubber member are suppressed. The tire 50 has high run-flat durability.

  Similar to the tire 2 in FIG. 1, the support layer 72 having a small calorific value can be made thinner than the conventional support layer 72. The thickness of the buttress portion of the tire 50 is substantially equal to or less than the thickness of the bead 60 portion. In the tire 50, the mass, rolling resistance, and vertical spring constant are reduced as compared with the conventional run flat tire. Further, in the present tire 50, by reducing the thickness of the buttress portion, a large deformation of the bead 60 portion is suppressed as compared with the conventional run flat tire. Thereby, the fall of durability by destruction of 60 parts of beads is controlled. According to the present invention, a pneumatic tire 50 with improved run flat durability and reduced mass, rolling resistance, and longitudinal spring constant compared to a conventional run flat tire can be obtained.

  Further, in the tire 50, turbulence is generated by the dimple 74 when the vehicle is traveling. This turbulent flow promotes heat radiation from the sidewall 56. Even when the tire 50 is in a puncture state, it is difficult to increase the temperature. In the tire 50, the rubber member is hardly broken or peeled off. For this reason, the thickness of the buttress portion is reduced by the dimple 74, but the durability of the tire 50 can be maintained. On the other hand, since the buttress portion is thin, the mass and rolling resistance of the tire 50 can be reduced. Further, the thin buttress portion contributes to the reduction of the longitudinal spring constant. In the tire 50, good fuel efficiency and riding comfort can be realized while maintaining run-flat durability.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A pneumatic tire (run flat tire) of Example 1 having the configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The tire size was 225 / 60R18. In this tire, the thickness T1 was 9.0 mm, and the thickness T2 was 10.2 mm.

[Comparative Example 1]
Comparative Example 1 is a run flat tire having a conventional load support layer.

[Comparative Example 2-4 and Example 2-4]
Tires of Comparative Example 2-4 and Example 2-4 were obtained in the same manner as in Example 1 except that the thickness T1 was changed and the ratio (T1 / T2) was changed as shown in Table 2.

[Comparative Example 5-6 and Example 5-8]
Tires of Comparative Example 5-6 and Example 5-8 were obtained in the same manner as Example 1 except that the loss tangent LT was changed as shown in Table 3.

[Examples 9-14]
A tire of Comparative Example 9-14 was obtained in the same manner as in Example 1 except that the complex elastic modulus E ^* was as shown in Table 4.

[Examples 15-19]
Tires of Examples 15-19 were obtained in the same manner as Example 1 except that the ratio (BH / H) was as shown in Table 5.

[Example 21]
A pneumatic tire (run flat tire) of Example 21 having the configuration shown in FIG. 3 and having the specifications shown in Table 6 below was obtained. This tire is the same as Example 1 except that a large number of dimples are added to the sidewall surface.

[Examples 20 and 22]
Tires of Examples 20 and 22 were obtained in the same manner as Example 21 except that the thickness (T1) was changed and the ratio (T1 / T2) was changed as shown in Table 6.

[Tire mass]
The mass of the tire was measured. The results are shown in Tables 1 to 6 below as index values with Example 1 as 100. It is shown that the smaller the numerical value, the smaller the mass. The smaller the value, the better.

[Evaluation of longitudinal spring constant]
The longitudinal spring constant of the tire was measured under the following conditions.
Rim used: 18 × 6.5J
Internal pressure: 180 kPa
Load: 5.0kN
The results are shown in Tables 1 to 6 below as index values with Example 1 as 100. The smaller the value, the lower the longitudinal rigidity. The smaller the value, the better.

[Rolling resistance]
Using a rolling resistance tester, rolling resistance was measured under the following measurement conditions.
Rim used: 18 × 6.5J
Internal pressure: 180 kPa
Load: 5.0kN
Speed: 80km / h
The results are shown in Tables 1 to 6 below as index values with Example 1 as 100. It shows that rolling resistance is so small that a numerical value is small. The smaller the value, the better.

[Durability (Runflat)]
The durability when the tire was punctured and the internal pressure decreased was evaluated as follows. The tire was assembled in a regular rim (18 × 6.5 J), and the tire was filled with air to adjust the internal pressure to 180 kPa. This tire was mounted on a drum-type running test machine, and a longitudinal load (7.5 kN) corresponding to 65% of the maximum load load of JATMA was applied to the tire. After that, the puncture state was reproduced with the internal pressure of the tire as normal pressure, and this tire was run on a drum having a radius of 1.7 m at a speed of 80 km / h. The distance traveled until the tire broke was measured. The results are shown in Tables 1 to 6 below as index values with Example 1 as 100. A larger numerical value is preferable.

  As shown in Tables 1 to 6, the tire of the example has a higher evaluation than the tire of the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The tire described above can be applied to various vehicles.

2, 50 ... Tire 4, 52 ... Tread 6, 54 ... Wing 8, 56 ... Sidewall 10, 58 ... Clinch 12, 60 ... Bead 14, 62 ... Carcass 14a ... Carcass ply 16, 64 ... Belt 16a ... Inner layer 16b ... Outer layer 18, 66 ... Band 20, 68 ... Inner liner 22, 70 ... Chafer 24, 72 ... Load supporting layer 26 ... Tread surface 28 ... Base layer 30 ... Cap layer 32 ... Groove 34 ... Core 36 ... Apex 38 ... Main part 40 ...・ Folding part 42 ... Inner end 44, 46 ... Outer end 48 ... End 74 ... Dimple 76 ... Land

Claims (4)

A tread whose outer surface forms a tread surface, a pair of sidewalls each extending substantially inward in the radial direction from the end of the tread, and a pair of clinch each positioned substantially inward in the radial direction from the sidewall, A pair of beads positioned on the inner side in the axial direction than the clinch, and a carcass spanned between one bead and the other bead along the inside of the tread and the sidewall, and each of which is more than the sidewall A pair of load support layers positioned on the inner side in the axial direction,
The loss tangent LT of the load support layer is 0.06 or more and 0.08 or less,
In a cross section perpendicular to the circumferential direction, the distance measured along the axial inner surface of the load support layer from the radially outer end to the inner end of the load support layer is L0, A point located on the side surface and having a distance (L0 / 3) from the radially outer end of the load supporting layer is P1, and when this tire is incorporated in the rim, the clinch and the flange of the rim When the point of the outer end of the contact portion is P2, the ratio (T1 / T2) of the thickness T1 from the outer surface to the inner surface of the tire at the point P1 to the thickness T2 from the outer surface to the inner surface of the tire at the point P2 A pneumatic tire that is 0.8 or more and 0.9 or less. The pneumatic tire according to claim 1, wherein the load supporting layer has a complex elastic modulus E ^* of 9 MPa or more and 11 MPa or less. The bead includes a core and an apex extending radially outward from the core;
When the point where the tire width is maximum on the outer surface of the sidewall is Pw, the height BH from the base line to the outer end of the apex in the radial direction is from the base line to the point Pw. The pneumatic tire according to claim 1 or 2, wherein a ratio (BH / H) to height H is 0.9 or more and 1.0 or less.   The pneumatic tire according to any one of claims 1 to 3, wherein a plurality of dimples are provided on a side surface that is a region that can be viewed from an axial direction in an outer surface of the tire.

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