pneumatic tires

Abstract

Pneumatic tires (1), comprising: a rubber reinforcement layer (10) arranged in sidewall sections (4) on both sides in a tire width direction, wherein the rubber reinforcement layer (10) has a distinct crescent-shaped meridian cross-section; wherein when the tire (1) is mounted on a conventional rim and in an unloaded state with an internal pressure of 0 kPa, a radius of curvature RP is smaller than the radius of curvature RO, an arc of radius of curvature RP connects an intersection point Pa of a carcass layer (6) and a straight line La, as well as an intersection point Pb of the carcass layer (6) and a straight line Lb and an intersection point Pc of the carcass layer (6) and a straight line Lc, and an arc of radius of curvature RO connecting an intersection point Oa of the line La and an outer tire contour, an intersection point Ob of a line Lb and the outer tire contour, and an intersection point Oc of the line Lc and the outer tire contour, wherein the line Lc is a line orthogonal to a tire equator plane (CL) at a part of the tire (1) with maximum width in a meridian cross-sectional view, the line La is a line of an intersection point of the line Lc and the tire equator plane (CL) inclined outwards by 10° in a tire radial direction with respect to the line Lc, and The line Lb is a line of intersection of the line Lc and the tire equator plane (CL), which is inclined inwards by 10° in the tire radial direction with respect to the line Lc, and a ratio between the radius of curvature RO and the radius of curvature RP, as follows, is sufficient: RO × 0.7 ≤ RP ≤ RO × 0.9, where the radius of curvature RP is from 40 to 65 mm, both inclusive.

Description

Technical field

[0001] The present invention relates to a pneumatic tire with run-flat properties. State of the art

[0002] Pneumatic tires are mounted on rims, inflated with air, and attached to a vehicle. When the vehicle moves, the load is supported by the internal air pressure. However, if the tire develops a puncture or similar issue, air escapes, rendering the tire unable to bear the load. More precisely, the load previously supported by the air pressure is then borne by the sidewalls, leading to significant deformation of these sections. This impairs the vehicle's ability to move.

[0003] There are pneumatic tires that address such problems. These tires have run-flat capabilities (allowing movement of the tire due to a puncture or similar issue) and are equipped with a rubber reinforcement layer on the inside of the sidewall sections, which increases their flexural rigidity. In other words, deformation of the sidewall sections is suppressed in these tires, allowing the tire to move even if some of the air has escaped and a significant load is being borne by the sidewalls.

[0004] Conventional tires, such as the pneumatic tire described in JP 2000 289409 A, are designed to enhance the performance of a run-flat tire by improving its cross-sectional shape and achieving an optimal cross-sectional shape that reduces the maximum load acting on the tire while minimizing the increase in tire weight. This pneumatic tire meets the following specifications: Ra / D≤0.08; Rb / D≤0.08; 0<φa≤50°;and 0<φb≤50°; wherein, in a standard tire axial cut where the tire is mounted on a standard wheel rim and inflated to a standard internal pressure and unloaded, Ra is the radius of curvature of a first arc with a center Oa on a tire axial direction line X, passing through a midpoint between the first point A and the second point B and on the inside of the tire cavity and in contact with the tire centerline at the first point A, wherein the first point A is a point where the tire radial direction line Y, passing through a wheel rim width position of the standard wheel rim, intersects the tire centerline passing through a midpoint of a tire thickness on a tread section side, and a second point B, which is a point where the tire radial direction line Y intersects the tire centerline on the tire bead section side.and Rb is a radius of curvature of a second arc with a center Ob on a tire axial direction line X and on the inside of the tire cavity and in contact with the tire centerline at the second point, and φa is an angle formed by the tire axial direction line X and the line Oa-A connecting the center Oa and the first point A, and φb is an angle formed by the tire axial direction line X and the line Ob-B connecting the center Ob and the second point B, and D is an outer diameter of the tire in its standard state.

[0005] DE 699 27 310 T2 discloses a pneumatic tire with excellent run-flat capability. The pneumatic tire has the size "215 / 65R15". The tire features a reinforcing strip of rubber with a crescent-shaped cross-section within a sidewall section. Furthermore, it is shown that the outer surfaces of the sidewall section have a convex shape in the area of ​​maximum tire width, with the radius of curvature from the carcass layer being smaller than the radius of curvature from the outer contour of the tire. DE 10 2013 202 009 A1 discloses a pneumatic tire of size “215 / 50RF17” which has a run-flat layer within sidewall sections. The run-flat layer has a crescent shape. It can be deduced that an outer surface of the sidewall section has a convex shape in the area of ​​the maximum tire width, with a radius of curvature of the carcass layer being smaller than a radius of curvature of the outer tire contour. EP 1 604 839 A1 discloses a tire of size “215 / 45ZR17”, with run-flat properties, which has a rubber reinforcement having a crescent shape and is provided on at least one inner surface of a sidewall section. It can be deduced that the outer surface of the sidewall section has a convex shape in the area of ​​the maximum tire width, wherein the radius of curvature of the carcass layer is smaller than the radius of curvature of the outer contour of the tire. EP 3 132 950 A1 discloses a tire of size “255 / 35R19”, with run-flat properties, which has a reinforcing rubber in sidewall sections with a crescent-shaped form in the tire width direction. It can be deduced that an outer surface of the sidewall section has a convex shape in the area of ​​the maximum tire width, wherein the radius of curvature of the carcass layer is smaller than the radius of curvature of the outer tire contour. US 2002 / 0 000 279 A1 discloses a tire comprising a carcass layer, a belt layer, and a bead core. The tire further comprises a first reinforcing layer and a second reinforcing layer, both having a crescent shape. The first reinforcing layer is positioned between the carcass layer and a folded section thereof and extends from an upper end of the bead core to near an end section of the belt layer. US 2012 / 0 298 280 A1 discloses a tire comprising a radial carcass reinforcement layer anchored in two beads around bead wires. The carcass reinforcement layer consists of a single layer of metal cords. Furthermore, the carcass reinforcement layer is wrapped with a crown reinforcement layer, which in turn is covered with a tread. US 2011 / 0 259 488 A1 discloses a pneumatic tire comprising a single reinforcing carcass layer extending from one bead section of the tire to an opposite bead section, and a sidewall insert located in each sidewall section of the tire. Brief description of the invention: Technical problem

[0006] However, run-flat tires are usually equipped with a thicker rubber reinforcement layer in the tire width direction to maintain good durability performance during run-flat operation (run-flat durability performance), with the thickness of the rubber reinforcement layer being increased in the tire width direction, which generally reduces driving comfort.

[0007] The present invention is based on the foregoing and an object of the present invention is to provide a pneumatic tire with both good run-flat durability performance and good driving comfort. Solution to the task

[0008] To solve the problem and achieve the described objective, the pneumatic tire of the invention comprises: a rubber reinforcement layer arranged in the sidewall sections on both sides in a tire width direction, wherein the rubber reinforcement layer has a substantially crescent-shaped meridian cross-section; wherein when the tire is mounted on a conventional rim and in an unloaded state with an internal pressure of 0 kPa, a radius of curvature RP is smaller than the radius of curvature RO, an arc of radius of curvature RP connects an intersection point Pa of a carcass layer and a straight line La, as well as an intersection point Pb of the carcass layer and a straight line Lb and an intersection point Pc of the carcass layer and a straight line Lc, and an arc of radius of curvature RO connecting an intersection point Oa of the straight line La and an outer tire contour, as well as an intersection point Ob of a straight line Lb and the outer tire contour and an intersection point Oc of the straight line Lc and the outer tire contour, wherein The line Lc is a perpendicular line to a tire equator plane at a part of the tire with maximum width in a meridian cross-sectional view. The line La is a line of intersection of the line Lc and the tire equatorial plane, which is inclined outwards by 10° in a tire radial direction with respect to the line Lc, and The line Lb is a line of intersection of the line Lc and the tire equator plane, which is inclined inwards by 10° in the tire radial direction with respect to the line Lc.

[0009] The radius of curvature RO of the arc connecting the points of intersection Oa, Ob, Oc of the lines La, Lb, Lc and the outer tire contour represents, in other words, the radius of curvature of the outer tire contour. The radius of curvature RP of the arc connecting the points of intersection Pa, Pb, Pc of the lines La, Lb, Lc and the carcass layer represents, in other words, the radius of curvature of the carcass layer. For a pneumatic tire where the radius of curvature RP of the carcass layer is smaller than the radius of curvature RO of the outer tire contour, the tensile strength in the radial direction of the carcass layer generally tends to decrease, while the vertical stiffness, i.e., the elasticity in the radial direction, increases. This allows for improved driving comfort while maintaining good run-flat durability performance, without reducing the cross-sectional thickness of the rubber reinforcement layer that enables run-flat operation.This results in both good emergency running durability performance and good driving comfort.

[0010] According to the invention, the ratio between the radius of curvature RO and the radius of curvature RP is as follows: RO × 0.7 ≤ RP ≤ RO × 0.9.

[0011] If the radius of curvature RP of the carcass layer is less than 0.4 times the radius of curvature RO of the outer tire contour, the vertical stiffness decreases significantly, and therefore no substantial improvement in run-flat durability is achieved. If the radius of curvature RP of the carcass layer is more than 0.9 times the radius of curvature RO, the vertical stiffness decreases, and the improvements in ride comfort are negligible. Accordingly, both good run-flat durability and good ride comfort are clearly achieved when the ratio RO × 0.7 ≤ RP ≤ RO × 0.9 is sufficient for the radii of curvature RO and RP.

[0012] Furthermore, according to the invention, the radius of curvature RP is between 40 and 65 mm, both inclusive.

[0013] If the radius of curvature (RP) of the carcass layer is less than 35 mm, the vertical stiffness decreases considerably, and the run-flat durability is therefore not substantially maintained. If the radius of curvature (RP) of the carcass layer is greater than 65 mm, the vertical stiffness decreases, rendering the improvements in ride comfort negligible. Accordingly, both good run-flat durability and good ride comfort are clearly achieved when the radius of curvature (RP) of the carcass layer is between 35 and 65 mm.

[0014] Furthermore, according to the invention, a ratio between a cross-sectional width Aip and a cross-sectional width Apo is satisfied as follows: Apo < Aip, wherein the cross-sectional width Aip is a cross-sectional width from an intersection point Ia of the line La and the inner tire contour to the intersection point Pa of the line La and the carcass layer within which the rubber reinforcement layer is arranged, and the cross-sectional width Apo is a cross-sectional width from the intersection point Pa to the intersection point Oa of the line La and the outer tire contour.

[0015] According to this pneumatic tire, where the cross-sectional width Aip is larger than the cross-sectional width Apo, the volume of the rubber reinforcement layer within the cross-sectional width Aip becomes relatively large, thus enabling improvements in run-flat durability performance.

[0016] Furthermore, according to the invention, the ratio between the cross-sectional width Aip and the cross-sectional width Apo is as follows: Apo × 4.4 ≤ Aip ≤ Apo × 6.0, and the cross-sectional width Aip is between 11.0 and 12.0 mm, both inclusive.

[0017] If the ratio Apo < Aip is such that the cross-sectional width Aip, within which the rubber reinforcement layer is located, is less than 1.5 times the cross-sectional width Apo, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 6.0 times the cross-sectional width Apo, the increase in vertical stiffness due to the rubber reinforcement layer is excessive, and therefore the improvements in ride comfort are negligible. If the cross-sectional width Aip is less than 5.0 mm, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 12.0 mm, the increase in vertical stiffness due to the rubber reinforcement layer is excessive, and therefore the improvements in ride comfort are negligible.Accordingly, with cross-sectional widths Aip, Apo with a ratio of Apo × 1.5 ≤ Aip ≤ Apo × 6.0 and cross-sectional width Aip between 5.0 and 12.0 mm, both inclusive, both good emergency running durability performance and driving comfort can be significantly achieved.

[0018] Furthermore, according to the invention, a ratio between a cross-sectional width Aip and a cross-sectional width Apo is satisfied as follows: Aip < Apo, wherein the cross-sectional width Aip is a cross-sectional width from an intersection point Ia of the line La and the inner tire contour to the intersection point Pa of the line La and the carcass layer within which the rubber reinforcement layer is arranged, and the cross-sectional width Apo is a cross-sectional width from the intersection point Pa to the intersection point Oa of the line La and the outer tire contour.

[0019] According to this pneumatic tire, where the cross-sectional width Aip is smaller than the cross-sectional width Apo, the volume of the rubber reinforcement layer within the cross-sectional width Aip becomes relatively small, thus enabling improvements in ride comfort.

[0020] Furthermore, according to the invention, the ratio between the cross-sectional width Aip and the cross-sectional width Apo is as follows: Apo × 0.77 ≤ Aip ≤ Apo × 0.9, and wherein the cross-sectional width Aip is between 6.2.0 and 9.0 mm, both inclusive.

[0021] If the ratio Apo < Aip is such that the cross-sectional width Aip, within which the rubber reinforcement layer is located, is less than 0.5 times the cross-sectional width Apo, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 0.9 times the cross-sectional width Apo, the increase in vertical stiffness due to the rubber reinforcement layer is excessive, and therefore the improvements in ride comfort are negligible. If the cross-sectional width Aip is less than 3.0 mm, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 9.0 mm, the increase in vertical stiffness due to the rubber reinforcement layer is excessive, and therefore the improvements in ride comfort are negligible.Accordingly, with cross-sectional widths Aip, Apo with a ratio of Apo × 0.5 ≤ Aip ≤ Apo × 0.9 and a cross-sectional width Aip between 3.0 and 9.0 mm, both inclusive, good emergency running durability performance and driving comfort can be achieved.

[0022] Furthermore, according to the invention, a ratio between the cross-sectional width Aip, the cross-sectional width Apo, a cross-sectional width Bip and a cross-sectional width Bpo is satisfied by the following: Bip / Bpo < Aip / Apo ≤ Bip / Bpo × 5.0, wherein the cross-sectional width Aip the cross-sectional width is from the intersection point Ia of the line La and the inner tire contour to the intersection point Pa of the line La and the carcass layer within which the rubber reinforcement layer is arranged, The cross-sectional width Apo is the cross-sectional width from the intersection point Pa to the intersection point Oa of the line La and the outer tire contour, the cross-sectional width Bip is a cross-sectional width from an intersection point Ib of the line Lb and the inner tire contour to the intersection point Pb of the line Lb and the carcass layer within which the rubber reinforcement layer is arranged, and the cross-sectional width Bpo is a cross-sectional width from the intersection point Pb to the intersection point Ob of the line Lb and the outer tire contour.

[0023] If the Bip / Bpo value is greater than that of Aip / Apo, the overall volume of the rubber reinforcement layer decreases, rendering improvements in run-flat durability negligible. If Aip / Apo is more than five times that of Bip / Bpo, the volume of the rubber reinforcement layer becomes relatively large in the tire's radial direction towards the outside, and the stiffness becomes excessively high, rendering improvements in ride comfort negligible. Accordingly, for cross-sectional widths Aip, Apo, Bip, and Bpo, a ratio of Bip / Bpo x 1.2 < Aip / Apo ≤ Bip / Bpo × 5.0 can achieve both good run-flat durability and good ride comfort.

[0024] According to an exemplary embodiment, the carcass cord threads of the carcass layer can be made of rayon.

[0025] According to the pneumatic tire, the use of rayon, a relatively light fiber with a relatively high tensile strength, allows the carcass cord threads of the carcass layer to achieve a tensile strength that results in significant improvements in run-flat durability performance in the tire radial direction of the carcass layer. Advantageous effects of the invention

[0026] The pneumatic tire according to the present invention can achieve both good run-flat durability performance and good driving comfort. Brief description of the drawings Fig. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. Fig. Figure 2 is an enlarged meridian cross-sectional view of a part of the pneumatic tire according to this embodiment of the present invention. Fig. Figure 3 is a table showing the performance test results of pneumatic tires according to embodiments of the present invention. Fig. Figure 4 is a table showing the performance test results of pneumatic tires according to embodiments of the present invention. Description of the embodiment

[0027] One embodiment of the present invention is described in detail below with reference to the drawings. However, the present invention is not limited to this embodiment. Furthermore, components of the embodiment include components that can be easily replaced by those skilled in the art or that are essentially identical to components of the embodiment. In addition, a multitude of modified examples described in the embodiment can be combined as needed, within the scope obvious to a person skilled in the art.

[0028] Fig. Figure 1 is a meridian cross-sectional view of a pneumatic tire according to the present embodiment. Fig. Figure 2 is an enlarged meridional cross-sectional view of a portion of the pneumatic tire according to the present embodiment.

[0029] In the following description, "tire radial direction" refers to a direction perpendicular to the axis of rotation (not shown) of a pneumatic tire 1. "Inward in the tire radial direction" refers to a side facing the axis of rotation in the tire radial direction, and "outward in the tire radial direction" refers to a side facing away from the axis of rotation in the tire radial direction. "Circular direction" refers to a circumferential direction with the axis of rotation as its central axis. "Width direction" also refers to a direction parallel to the axis of rotation. "Inward in the tire width direction" refers to a side facing a tire equator plane CL (tire equator line) in the tire width direction, and "outward in the tire width direction" refers to a side facing away from the tire equator plane CL in the tire width direction.“Tire equator plane CL” refers to a plane that is perpendicular to the axis of rotation of the pneumatic tire 1 and extends through the center of the pneumatic tire 1 in the tire width direction. “Tire width” is the width in the tire width direction between components located on the outer side in the tire width direction, or in other words, the distance between the components furthest from the tire equator plane CL in the tire width direction. “Tire equator line” refers to a line along the circumferential direction of the pneumatic tire 1 that lies on the tire equator plane CL. In the present embodiment, the same reference numeral CL is used for the tire equator line as for the tire equatorial plane. In addition, the pneumatic tire 1 described below has a substantially symmetrical structure with respect to the tire equator plane CL. Therefore, the pneumatic tire 1 is described in meridian cross-sectional view ( Fig. 1) shown, along a plane passing through the axis of rotation of the pneumatic tire 1, and with respect to the structure only one side (right side in Fig. 1) The tire equator plane CL is described. A description of the other side (left side in Fig. 1) is omitted.

[0030] As in Fig. As shown in Figure 1, the pneumatic tire 1 of the present embodiment comprises a tread section 2 and shoulder sections 3 on both sides of the tread section 2. The pneumatic tire 1 further comprises sidewall sections 4 and bead sections 5, arranged in that order from the shoulder sections 3. The pneumatic tire 1 also comprises a carcass layer 6, a belt layer 7, a belt reinforcement layer 8, an inner layer 9, and a rubber reinforcement layer 10.

[0031] The tread section 2 is made of tread rubber 2A and is exposed on its outermost side in the radial direction of the pneumatic tire 1; its surface forms the contour of the pneumatic tire 1. A tread surface 21 is formed on an outer circumferential surface of the tread section 2, or in other words, on a road contact surface that comes into contact with a road surface when driving. The tread surface 21 is provided with a plurality (four in the present embodiment) of main grooves 22 extending in the circumferential direction of the tire. The main grooves 22 are straight main grooves that run parallel to the tire equator line CL. Furthermore, a plurality of rib-like web sections 23 are formed in the tread surface 21, extending in the circumferential direction of the tire and defined by the plurality of main grooves 22.It should be noted that the main grooves 22 may be curved or bent in the direction of the tire's circumference. Additionally, lug grooves running in a direction that intersects the tire's circumference are provided in the rib sections 23 of the tread surface 21. The lug grooves may intersect the main grooves 22. Alternatively, the lug grooves may have an end that does not intersect the main grooves 22 and terminates in a rib section 23. If both lug grooves have ends that intersect the main grooves 22, the rib sections 23 form a multitude of block-like rib sections that are subdivided in the direction of the tire's circumference. It should be noted that the lug grooves may be angled with respect to the tire's circumference, and may be curved or bent.

[0032] The shoulder sections 3 are areas on both outer sides of the tread section 2 in the tire width direction. In other words, the shoulder sections 3 are made of tread rubber 2A. Additionally, the sidewall sections 4 are exposed on the outermost side of the pneumatic tire 1 in the tire width direction. The sidewall sections 4 are made of sidewall rubber 4A. The tire bead sections 5 each include a tire bead core 51 and a tire bead filler 52. The tire bead core 51 is formed by winding a bead wire, which is a steel wire, into a ring shape. The tire bead filler 52 is a rubber material arranged in a cavity formed by folding back one end of the carcass layer 6 in the tire width direction at the position of the tire bead core 51. Each tire bead section 5 includes an outwardly exposed rim pad rubber 5A that comes into contact with the rim (not shown).The rim padding rubber 5A forms the outer circumference of the tire bead section 5. The rim padding rubber 5A is positioned inwards from the tire bead section 5 and completely covers the outwards tire bead filler 52 (sidewall section 4) by extending over the lower end of the tire bead section 5.

[0033] The ends of the carcass layer 6 in the tire width direction are folded from the inside in the tire width direction to the outside in the tire width direction around the pair of tire bead cores 51, and the carcass layer 6 is stretched in the tire circumferential direction into an annular shape to form the tire frame. The carcass layer 6 is formed from a plurality of carcass cord threads with a rubber coating (not shown) arranged parallel to each other in the tire circumferential direction along a tire meridian direction at a predetermined angle with respect to the tire circumferential direction. The carcass cord threads are made of organic fibers (e.g., polyester, rayon, nylon, or the like). The carcass layer 6 is provided with at least one layer and, in the present embodiment, with two layers. As shown in Fig. As shown in Figure 1, the end section of the inner layer of the two carcass layers 6 extends to the sidewall section 4 and covers the entire tire bead filler 52, while the end section of the outer layer extends to a position where the tire bead filler 52 is only partially covered.

[0034] The belt layer 7 has a multi-layered structure, with at least two layers (belts 71 and 72) superimposed. Belt layer 7 is arranged radially outward in the tread section 2, corresponding to the outer circumference of the carcass layer 6, and covers the carcass layer 6 circumferentially. Belts 71 and 72 comprise a plurality of rubber-coated cord threads (not shown) arranged parallel at a predetermined angle to the tire's circumferential direction (e.g., between 20° and 30°). The cord threads are made of organic fibers (e.g., polyester, rayon, nylon, or the like). Furthermore, belts 71 and 72 overlap each other and are arranged so that the respective belts intersect.

[0035] The belt reinforcement layer 8 is arranged radially outwards in the tire direction, corresponding to the outer circumference of the belt layer 7, and covers the belt layer 7 in the tire circumferential direction. The belt reinforcement layer 8 comprises a plurality of rubber-coated cord threads (not shown) arranged parallel in the tire width direction and substantially parallel (± 5°) in the tire circumferential direction. The cord threads are made of organic fibers (e.g., polyester, rayon, nylon, or the like). Fig. The belt reinforcement layer 8 shown in Figure 1 comprises two layers, one of which covers the entire belt layer 7 and the other of which covers the end sections of the belt layer 7 in the tire width direction. The configuration of the belt reinforcement layer 8 is not limited to that described above. Although not shown in the drawings, a configuration can be used in which, for example, the two layers are arranged to cover the entire belt layer 7, or in which the two layers are arranged to cover only the end sections of the belt layer 7 in the tire width direction.Additionally, although not shown in the drawings, a configuration of the belt reinforcement layer 8 can be used in which, for example, one layer is arranged to cover the entire belt layer 7, or in which one layer is arranged to cover only the end sections of the belt layer 7 in the tire width direction. In other words, the belt reinforcement layer 8 overlaps at least the end sections of the belt layer 7 in the tire width direction. Furthermore, the belt reinforcement layer 8 is provided by winding a ribbon-shaped strip material (e.g., with a width of 10 mm) in the tire circumferential direction.

[0036] The inner layer 9 is the inner surface of the tire, i.e., the inner circumferential surface of the carcass layer 6. Both ends of the inner layer 9, in the tire width direction, extend to the tire bead cores 51 of the tire bead sections 5 and extend in a ring-shaped manner in the tire circumference direction. The inner layer 9 prevents air molecules from escaping the tire. It should be noted that, as in Fig. As shown in Figure 1, the inner layer 9 can be arranged so that it extends inwards from the tire bead section 5. However, the inner layer 9 can also be arranged so that it extends from the lower section (inwards in the tire radial direction) of the tire bead core 51.

[0037] The rubber reinforcement layer 10 is located within the sidewall section 4 and is not exposed to the inside or outside. The rubber reinforcement layer 10 is primarily positioned between the carcass layer 6 and the inner layer 9, corresponding to the inside of the carcass layer 6, and has a crescent-shaped meridian cross-section. The rubber reinforcement layer 10 is formed from a rubber material whose thickness is greater than that of the rim pad rubber 5A of the tire bead sections 5 or than that of the sidewall rubbers 4A of the sidewall sections 4. The rubber reinforcement layer 10 may be formed from a different rubber material and may be positioned between the carcass layer 6 and the sidewall rubber 4A and the rim pad rubber 5A, corresponding to the outside of the tire carcass layer 6, as shown in [Figure / Figure]. Fig. 1 shown.

[0038] The pneumatic tire 1 is mounted on a vehicle (not shown) with the tire bead sections 5 resting on the rim and inflated to a predetermined air pressure. When the vehicle moves, the tread surface 21 comes into contact with the road surface while the pneumatic tire 1 rotates. As the vehicle moves, the tread surface 21 bears a load, including the weight of the vehicle, due to the contact described above. When the tread surface 21 bears such a load, the pneumatic tire 1 deforms elastically in a manner corresponding to the nature of the load and the rigidity of the tire components, and the air with which the tire is inflated acts on the inside of the tire to expand it outwards.The spring force provided by the air with which the tire is inflated prevents excessive deformation of the pneumatic tire 1, even when the tread surface 21 bears a load. Accordingly, the pneumatic tire 1 can rotate while carrying a load, thus enabling the vehicle to move.

[0039] Although the pneumatic tire 1 does not easily deform during vehicle movement due to the air pressure from the air with which it is inflated, a foreign material can puncture the tread surface 21 and, for example, cause a hole in the tire, thus allowing air to escape from the pneumatic tire 1. As air escapes from the inside of the pneumatic tire 1, the spring force acting on the inside of the pneumatic tire 1 to expand it outwards decreases. If the tread surface 21 of the flat pneumatic tire 1 bears a load, the load is borne in the tire's radial direction by the sidewall sections 4. This makes the sidewall sections 4 susceptible to elastic deformation in the tire's radial direction. However, these sidewall sections 4 are reinforced with rubber reinforcement layers 10.As previously described, the rubber reinforcement layer 10 is made of a rubber material whose thickness is greater than that of the sidewall rubber 4A of the sidewall sections 4. Accordingly, the rubber reinforcement layer 10 suppresses the deformation of the sidewall sections 4 in the tire radial direction when the sidewall sections 4 bear a load in the tire radial direction. Thus, due to the rubber reinforcement layer 10, which prevents the deformation of the sidewall sections 4 in the tire radial direction, the pneumatic tire 1 enables the movement of the vehicle or run-flat driving (movement with the pneumatic tire 1 in a flat state).

[0040] If such a run-flat tire 1 is mounted on a conventional rim in an unloaded state with an internal pressure of 0 kPa, a straight line perpendicular to a tire equator plane CL at a portion of the tire with maximum width, viewed in a meridian cross-section, is considered to be line Lc. Additionally, a line at an intersection point Q of line Lc and the tire equator plane CL, inclined outwards at an angle θ1 of 10° with respect to line Lc in the tire radial direction, is considered to be line La, and a line inclined inwards at an angle θ2 of 10° in the tire radial direction is considered to be line Lb.As defined, a radius of curvature RP of an arc connecting the points of intersection Pa, Pb, Pc of the respective lines La, Lb, Lc with the carcass layer 6 is smaller than the radius of curvature RO of an arc connecting the points of intersection Oa, Ob, Oc of the respective lines La, Lb, Lc with the outer tire contour.

[0041] It should be noted that the intersection points Pa, Pb, Pc are the points where the midpoint of the carcass cord threads of the innermost carcass layer 6 and the respective straight lines La, Lb, Lc intersect.

[0042] Here, "conventional rim" refers to a "standard rim" as defined by the Japan Automobile Tyre Manufacturers Association (JATMA), a "design rim" as defined by the Tire and Rim Association (TRA), or a "measuring rim" as defined by the European Tyre and Rim Technical Organisation (ETRTO). "Regular internal pressure" refers to a "maximum air pressure" as defined by JATMA, a specified maximum value in "tire load limits at various cold inflation pressures" as defined by the TRA, or "inflation pressures" as defined by the ETRTO.It should be noted that the “regular load” refers to a “maximum load capacity” as defined by JATMA, a specified maximum value in “tire load limits at various cold inflation pressures” as defined by TRA, or a “load capacity” as defined by ETRTO.

[0043] The portion of the tire with maximum width is the position of the edges of the tire's cross-sectional width, with the width being greatest in the tire's width direction. The tire's cross-sectional width in the present embodiment is equal to the maximum overall width of the tire in the tire's width direction, less the width of any patterns, letters, or the like, when the pneumatic tire 1 is mounted on a conventional rim and in an unloaded state with an internal pressure of 0 kPa. For tires provided with a rim protector (provided along the tire's radial direction and projecting outwards in the tire's circumferential direction) to protect the rim, the rim protector represents the portion furthest outwards in the tire's width direction, and the cross-sectional width in this embodiment does not include the rim protector.Additionally, the "outer tire contour" refers to the profile of the pneumatic tire 1, excluding any patterns or letters corresponding to the outer surface of the pneumatic tire 1. "Outer tire contour" refers to the profile corresponding to the inner layer 9, which is the inner surface of the pneumatic tire 1.

[0044] The radius of curvature RO of the arc connecting the intersection points Oa, Ob, Oc of the lines La, Lb, Lc and the outer tire contour represents, in other words, the radius of curvature of the outer tire contour. The radius of curvature RP of the arc connecting the intersection points Pa, Pb, Pc of the lines La, Lb, Lc and the carcass layer 6 represents, in other words, the radius of curvature of the carcass layer 6. According to the pneumatic tire 1, where the radius of curvature RP of the carcass layer 6 is smaller than the radius of curvature RO of the outer tire contour, the tensile strength in the radial direction of the carcass layer 6 generally tends to decrease, and the vertical stiffness, i.e., the elasticity in the radial direction, increases. This allows driving comfort to be improved while maintaining good run-flat properties without reducing the cross-sectional thickness of the rubber reinforcement layer 10, which contributes to enabling run-flat movement.This results in both good emergency running durability performance and good driving comfort.

[0045] In the pneumatic tire 1 of the present embodiment, the ratio of the radii of curvature RO, RP is preferably such that RO × 0.4 ≤ RP ≤ RO × 0.9 is sufficient.

[0046] If the radius of curvature RP of the carcass layer 6 is less than 0.4 times the radius of curvature RO of the outer tire contour, the vertical stiffness decreases significantly, and therefore no substantial improvement in run-flat durability is achieved. If the radius of curvature RP of the carcass layer 6 is more than 0.9 times the radius of curvature RO of the outer tire contour, the decrease in vertical stiffness is negligible, and therefore the improvements in ride comfort are negligible. Accordingly, both good run-flat durability and good ride comfort are clearly achieved when the ratio RO × 0.4 ≤ RP ≤ RO × 0.9 satisfies the radii of curvature RO and RP. It should be noted that to achieve significant emergency running durability and driving comfort, the ratio RO × 0.5 ≤ RP ≤ RO × 0.8 should preferably suffice.

[0047] In the pneumatic tire 1 of the present embodiment, the radius of curvature RP of the carcass layer 6 is preferably between 35 and 65 mm, both inclusive.

[0048] If the radius of curvature RP of the carcass layer 6 is less than 35 mm, the vertical stiffness decreases considerably, and the run-flat durability performance is therefore not substantially maintained. If the radius of curvature RP of the carcass layer 6 is greater than 65 mm, the decrease in vertical stiffness is negligible, and therefore the improvements in ride comfort are negligible. Accordingly, both good run-flat durability performance and good ride comfort are clearly achieved when the radius of curvature RP of the carcass layer 6 is between 35 and 65 mm, inclusive.

[0049] The pneumatic tire 1 of this present embodiment is provided with a rubber reinforcement layer 10 within a cross-sectional width Aip, which results from the intersection point Ia of the line La and the inner tire contour with the intersection point Pa of the line La and the carcass layer 6. A cross-sectional width Apo results from the intersection point Pa with the intersection point Oa of the line La and the outer tire contour. Defined as such, the ratio between the cross-sectional width Aip and the cross-sectional width Apo, preferably Apo < Aip, is sufficient.

[0050] According to this pneumatic tire 1, where the cross-sectional width Aip is larger than the cross-sectional width Apo, the volume of the rubber reinforcement layer 10 within the cross-sectional width Aip becomes relatively large and therefore makes it possible to achieve improvements in run-flat durability performance.

[0051] In the pneumatic tire 1 of the present embodiment, the ratio between the cross-sectional widths Aip, Apo preferably Apo × 1.5 ≤ Aip ≤ Apo × 6.0 is sufficient, and the cross-sectional width Aip preferably ranges from 5.0 to 12.0 mm, both inclusive.

[0052] If the ratio Apo < Aip is such that the cross-sectional width Aip, within which the rubber reinforcement layer 10 is arranged, is less than 1.5 times the cross-sectional width Apo, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 6.0 times the cross-sectional width Apo, the increase in vertical stiffness due to the rubber reinforcement layer 10 is excessive, and therefore the improvements in ride comfort are negligible. If the cross-sectional width Aip is less than 5.0 mm, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 12.0 mm, the increase in vertical stiffness due to the rubber reinforcement layer 10 is excessive, and therefore the improvements in ride comfort are negligible.Accordingly, with cross-sectional widths Aip, Apo with a ratio of Apo × 1.5 ≤ Aip ≤ Apo × 6.0 and a cross-sectional width Aip of 5.0 to 12.0 mm, both good emergency running durability performance and driving comfort can be significantly achieved.

[0053] The pneumatic tire 1 of this present embodiment is provided with a rubber reinforcement layer 10 within the cross-sectional width Aip, which is defined by the intersection point Ia of the line La and the inner tire contour with the intersection point Pa of the line La and the carcass layer 6. The cross-sectional width Apo is defined by the intersection point Pa with the intersection point Oa of the line La and the outer tire contour. Defined as such, the ratio between the cross-sectional width Aip and the cross-sectional width Apo, from another perspective, preferably Aip < Apo, is sufficient.

[0054] According to this pneumatic tire 1, where the cross-sectional width Aip is smaller than the cross-sectional width Apo, the volume of the rubber reinforcement layer 10 within the cross-sectional width Aip becomes relatively small, thus enabling improvements in ride comfort.

[0055] In the pneumatic tire 1 of the present embodiment, the ratio between the cross-sectional widths Aip, Apo preferably Apo × 0.5 ≤ Aip ≤ Apo × 0.9 is sufficient, and the cross-sectional width Aip preferably ranges from 3.0 to 9.0 mm, both inclusive.

[0056] If the ratio Aip < Apo is such that the cross-sectional width Aip, within which the rubber reinforcement layer 10 is arranged, is less than 0.5 times the cross-sectional width Apo, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 0.9 times the cross-sectional width Apo, the increase in vertical stiffness due to the rubber reinforcement layer 10 is excessive, and therefore the improvements in ride comfort are negligible. If the cross-sectional width Aip is less than 3.0 mm, the improvements in run-flat durability are negligible. If the cross-sectional width Aip is more than 9.0 mm, the increase in vertical stiffness due to the rubber reinforcement layer 10 is excessive, and therefore the improvements in ride comfort are negligible.Accordingly, with cross-sectional widths Aip, Apo with a ratio of Apo × 0.5 ≤ Aip ≤ Apo × 0.9 and a cross-sectional width Aip of 3.0 to 9.0 mm, both inclusive, good emergency running durability performance and driving comfort can be achieved.

[0057] The pneumatic tire 1 of this present embodiment is provided with a rubber reinforcement layer 10 within the cross-sectional width Aip, which is determined by the intersection point Ia of the line La and the inner tire contour with the intersection point Pa of the line La and the carcass layer 6. The cross-sectional width Apo is determined by the intersection point Pa with the intersection point Oa of the line La and the outer tire contour. The rubber reinforcement layer 10 is provided with a cross-sectional width Bip, which is determined by the intersection point Ib of the line Lb and the inner tire contour with the intersection point Pb of the line Lb and the carcass layer 6. The cross-sectional width Bpo is determined by the intersection point Pb with the intersection point Ob of the line Lb and the outer tire contour. Defined as such, the ratio of the cross-sectional widths Aip, Apo, Bip, and Bpo preferably satisfies Bip / Bpo < Aip / Apo ≤ Bip / Bpo × 5.0.

[0058] If the Bip / Bpo ratio is greater than that of Aip / Apo, the overall volume of the rubber reinforcement layer 10 decreases, rendering improvements in run-flat durability insignificant. If Aip / Apo is more than 5.0 times the Bip / Bpo ratio, the volume of the rubber reinforcement layer 10 becomes relatively large in the radial direction towards the outside of the tire, and the stiffness becomes excessively high, rendering improvements in ride comfort insignificant. Accordingly, for the cross-sectional widths Aip, Apo, Bip, and Bpo, a Bip / Bpo ratio < Aip / Apo ≤ Bip / Bpo × 5.0 achieves both good run-flat durability and good ride comfort.

[0059] In addition, the carcass cord threads of the carcass layer 6 in the pneumatic tire 1 of the present embodiment are preferably made of rayon.

[0060] According to the pneumatic tire 1, the use of rayon, a relatively light fiber with a relatively high tensile strength, enables the carcass cord threads of the carcass layer 6 to achieve a tensile strength which, in the tire radial direction of the carcass layer 6, achieves significant improvements in run-flat durability performance. Examples of implementation

[0061] In the exemplary embodiments, performance tests regarding run-flat durability and ride comfort were carried out with a variety of pneumatic tire types under different conditions (see Fig. 3 and Fig. 4).

[0062] The tests used pneumatic tires (test tires) of size 235 / 50R18, mounted on a conventional rim 18 × 7.5J.

[0063] The run-flat durability test was conducted using test tires with an internal pressure of 0 kPa on a test track in accordance with Regulation 30 of the Economic Commission for Europe (ECE). The distance traveled results were indexed to the results of Conventional Example 1 and Conventional Example 2, which were set as the standard (100). The higher the index value, the greater the distance traveled and therefore the higher the run-flat durability.

[0064] The ride comfort evaluation test included a sensory assessment by a test driver after driving a test vehicle (a 2000 cc SUV manufactured in Japan) equipped with the test tires on a test track. The test tires were inflated to the specified internal pressure. The results were indexed to the results of Conventional Example 1 and Conventional Example 2, which were set as the standard (100). A higher index value indicates greater ride comfort.

[0065] As in Fig. 3 and Fig. As shown in Figure 4, the ratio of the radius of curvature RO to the radius of curvature RP is not specified in detail for the pneumatic tires of Conventional Example 1 and Conventional Example 2. In contrast to the pneumatic tires of Conventional Example 1, the ratio of the radius of curvature RO to the radius of curvature RP and other ratios are specified for the pneumatic tires of embodiments 1 to 13. Additionally, in contrast to the pneumatic tires of Conventional Example 2, the ratio of the radius of curvature RO to the radius of curvature RP and other ratios are specified for the pneumatic tires of embodiments 14 to 24.

[0066] How the test results in Fig. 3 and Fig. As shown in Figure 4, the pneumatic tires of embodiments 1 to 24 achieve both good run-flat durability performance and driving comfort. List of reference symbols 1 pneumatic tire 4 Side wall section 6 Carcass layer 10 Rubber reinforcement layer CL tire equator plane

Claims

[1] Pneumatic tyre (1), comprising: a rubber reinforcing layer (10) arranged in sidewall portions (4) on both sides in a tire width direction, the rubber reinforcing layer (10) having a substantially crescent-shaped meridian cross-section; wherein when the tire (1) is mounted on a conventional rim and in an unloaded state with an internal pressure of 0 kPa, a radius of curvature RP is smaller than the radius of curvature RO, an arc of curvature radius RP connects an intersection point Pa of a carcass layer (6) and a straight line La as well as an intersection point Pb of the carcass layer (6) and a straight line Lb and an intersection point Pc of the carcass layer (6) and a straight line Lc, and an arc of curvature radius RO connecting an intersection point Oa of the straight line La and an outer tire contour and an intersection point Ob of a straight line Lb and the outer tire contour and an intersection point Oc of the straight line Lc and the outer tire contour, wherein the straight line Lc is a straight line orthogonal to a tire equatorial plane (CL) at a part of the tire (1) having a maximum width in a meridian cross-sectional view, the straight line La is a straight line of an intersection point of the straight line Lc and the tire equatorial plane (CL) which is inclined outward by 10° in a tire radial direction with respect to the straight line Lc, and the straight line Lb is a straight line of an intersection point of the straight line Lc and the tyre equatorial plane (CL), which is inclined inwards by 10° in the tyre radial direction with respect to the straight line Lc, and a ratio between the radius of curvature RO and the radius of curvature RP satisfying: RO × 0.7 ≤ RP ≤ RO × 0.9, where the radius of curvature RP is from 40 to 65 mm, both inclusive. [2] Pneumatic tire (1) according to claim 1, further comprising: a ratio between a cross-sectional width Aip and a cross-sectional width Apo satisfies the following: Apo < Aip, where the section width Aip is a section width from an intersection point Ia of the straight line La and an inner tire contour to the intersection point Pa of the straight line La and the carcass layer within which the rubber reinforcing layer is arranged, and the section width Apo is a section width from the intersection point Pa to the intersection point Oa of the straight line La and the outer tyre contour; and the ratio between the section width Aip and the section width Apo satisfies the following: Apo × 4.4 ≤ Aip ≤ Apo × 6.0, and the section width Aip is between 11.0 and 12.0 mm, both inclusive. [3] Pneumatic tire (1) according to claim 1 or 2, further comprising: a ratio between a cross-sectional width Aip and a cross-sectional width Apo satisfies the following: Aip <Apo, where the cross-sectional width Aip is a cross-sectional width from an intersection point Ia of the straight line La and an inner tire contour to the intersection point Pa of the straight line La and the carcass layer (6) within which the rubber reinforcing layer (10) is arranged, and the section width Apo is a section width from the intersection point Pa to the intersection point Oa of the straight line La and the outer tire contour; and the ratio between the cross-sectional width Aip and the cross-sectional width Apo satisfies the following: Apo×0.77≤Aip≤Apo×0.9, and wherein the cross-sectional width Aip is between 6.2 and 9.0 mm, both inclusive. [4] A pneumatic tire according to any one of claims 1 to 3, further comprising: a ratio between the cross-sectional width Aip, the cross-sectional width Apo, a cross-sectional width Bip and a cross-sectional width Bpo satisfies the following: Bip / Bpo×1.2≤Aip / Apo≤Bip / Bpo×5.0, where the cross-sectional width Bip is a cross-sectional width from an intersection point Ib of the straight line Lb and the inner tire contour to the intersection point Pb of the straight line Lb and the carcass layer (6) within which the rubber reinforcing layer (10) is arranged, and the section width Bpo is a section width from the intersection point Pb to the intersection point Ob of the straight line Lb and the outer tire contour. [5] A pneumatic tire (1) according to any one of claims 1 to 4, wherein the carcass cords of the carcass layer (6) are made of rayon.

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