JP6801488B2 - Pneumatic tires - Google Patents

Description

The present invention relates to a pneumatic tire. In particular, the invention relates to side reinforced run-flat tires.

In recent years, run-flat tires with a support layer inside the sidewall have been developed and are becoming widespread. High hardness crosslinked rubber is used for this support layer. This run-flat tire is called a side reinforcement type.

In this type of run-flat tire, when the internal pressure drops due to a flat tire, the support layer supports the vehicle weight. With run-flat tires, it is possible to run a certain distance even in a flat tire. Various studies have been conducted on run-flat tires. An example of this study is disclosed in Japanese Patent Application Laid-Open No. 2015-067256.

JP-A-2015-067256

A load is periodically applied to the tire in the running state. As a result, deformation and restoration are repeated. In a run-flat tire, the degree of deformation of the bead part is large, and when running in a punctured state (hereinafter, also referred to as run-flat running), the bead part is damaged instead of the sidewall part. There is.

The apex with a large width contributes to the rigidity of the bead portion. If this apex is adopted, the deformation of the bead part can be suppressed. Suppression of deformation contributes to damage prevention. Apex is laminated on the core. Therefore, the width of the apex is constrained by the width of the core. Adjusting the width of the apex may not allow sufficient control of rigidity.

The long apex also contributes to the rigidity of the bead part. Apex usually has a tapered shape. Therefore, the contribution of the tip of Apex to the rigidity is surprisingly small. With a long apex, the deformation of the bead part may not be sufficiently suppressed.

In tires, stress tends to be concentrated on the part that comes into contact with the rim. In run-flat running, the tire is repeatedly deformed and restored. This part tends to get hot. Heat generation can impair durability.

In run-flat tires, high-hardness crosslinked rubber is used for the support layer. Therefore, this tire is heavier than a tire that does not have this support layer. Large mass affects rolling resistance.

An object of the present invention is to provide a pneumatic tire in consideration of weight reduction and reduction of rolling resistance while improving durability in run-flat running.

The pneumatic tire according to the present invention includes a tread, a pair of sidewalls, a pair of clinches, a pair of beads, a carcass, a pair of support layers and a pair of cushioning layers. Each sidewall extends substantially inward in the radial direction from the end of the tread. Each clinch extends substantially inward in the radial direction from the edge of the sidewall. Each bead is located axially inside the clinch. The carcass spans between one bead and the other along the inside of the tread and sidewalls. Each support layer is located axially inward of the sidewall. Each buffer layer is located between the carcass and the clinch. The bead includes a core and an apex, and the apex extends substantially outward in the radial direction from the core, and the length of the apex is 20 mm or less. The outer edge of the buffer layer is located radially inside the maximum width position of the tire. In the radial direction, the position of the inner edge of the buffer layer coincides with the position of the outer edge of the core, or the inner edge of the buffer layer is located outside the outer edge of the core. The ratio of the radial distance from the bead baseline to the outer edge of the buffer layer to the radial distance from the bead baseline to the outer edge of the clinch is 85% or more and 105% or less. When the position on the outer surface of the tire where the radial height from the bead baseline is 14 mm is the first point P1 and the position where the radial height from the bead baseline is 20 mm is the second point P2. In the radial direction, the buffer layer overlaps each of the first point P1 and the second point P2. The loss tangent of the buffer layer is equal to or less than the loss tangent of the clinch and the loss tangent of the apex. The hardness of the buffer layer is equal to or higher than the hardness of the apex.

Preferably, in this pneumatic tire, the loss tangent of the buffer layer is equal to or less than the loss tangent of the support layer.

Preferably, in this pneumatic tire, when the normal of the outer surface of the tire at the second point P2 is used as the reference normal, each of the buffer layer and the clinch measured along the reference normal. The thickness is 1 mm or more.

Preferably, in this pneumatic tire, the total thickness of the buffer layer thickness and the clinch thickness measured along the reference normal is the support layer measured along the reference normal. The ratio to the thickness is 80% or more and 120% or less.

In the pneumatic tire according to the present invention, a small apex is adopted. In this tire, the apex is placed outside the area where the strain is concentrated in the punctured state. With this tire, the deformation of Apex is effectively suppressed.

In this tire, a cushioning layer is provided between the carcass and the clinch. This buffer layer does not easily generate heat and is hard.

In this tire, the cushioning layer is arranged in an appropriate position and in an appropriate size in consideration of the area where strain is concentrated. The hard cushioning layer suppresses deformation of the bead portion not only during normal running but also when the internal pressure is lowered due to a puncture. In this tire, heat generation due to deformation of the bead portion is effectively suppressed. In particular, heat generation between the contact surface with the rim and the carcass is suppressed. Moreover, in this tire, the cushioning layer itself does not easily generate heat, so that heat generation can be suppressed quite effectively in the bead portion. The cushioning layer also places the carcass at the bead portion axially inward of that of a conventional tire without this cushioning layer. Distortion is less likely to concentrate on this carcass. In this tire, the occurrence of damage in the bead part is effectively suppressed.

This tire uses a small apex, and by arranging a hard and heat-resistant cushioning layer at an appropriate position and an appropriate size, it runs in a state where the internal pressure is reduced due to a flat tire, that is, run-flat. During running, damage to the bead portion is effectively suppressed. With this tire, a sufficient mileage is secured even when the internal pressure is lowered due to a flat tire. This tire has excellent durability in run-flat running.

In this tire, the synergistic action of the apex and the cushioning layer suppresses the occurrence of damage at the bead portion, so that the volume of the support layer can be reduced. This reduction in the volume of the support layer contributes to the weight reduction of the tire and the reduction of rolling resistance. With this tire, weight reduction and reduction of rolling resistance can be achieved while improving durability during run-flat running. According to the present invention, it is possible to obtain a pneumatic tire in which weight reduction and reduction of rolling resistance are taken into consideration while improving durability in run-flat running.

FIG. 1 is a cross-sectional view showing a part of a pneumatic 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.

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

FIG. 1 shows the pneumatic tire 2. In FIG. 1, the vertical direction is the radial direction of the tire 2, the left-right 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, the alternate long and short dash line CL represents the equatorial plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equatorial plane except for the tread pattern. FIG. 1 shows a cross section of the tire 2 along a plane including a rotation axis of the tire 2.

In FIG. 1, the tire 2 is incorporated in the rim R. This rim R is a regular rim. The tire 2 is filled with air. As a result, the internal pressure of the tire 2 is adjusted to the normal internal pressure.

Unless otherwise specified, the dimensions and angles of each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. When the tire 2 is for a passenger car, the dimensions and angles are measured with an internal pressure of 180 kPa unless otherwise specified.

As used herein, the term "regular rim" means a rim defined in the standard on which Tire 2 relies. The "standard rim" in the JATTA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

As used herein, the normal internal pressure means the internal pressure defined in the standard on which the tire 2 relies. The "maximum air pressure" in the JATTA standard, the "maximum value" in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

In the present specification, the normal load means the load defined in the standard on which the tire 2 relies. The "maximum load capacity" in the JATMA standard, the "maximum value" in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

In FIG. 1, the solid BBL is a bead baseline. This bead baseline is a line that defines the rim diameter (see JATTA standard, etc.) of the rim R on which the tire 2 is mounted. This bead baseline extends axially.

In FIG. 1, the symbol PE is an intersection of the outer surface of the tire 2 and the equator surface. This intersection PE is also called the equator. This intersection PE is also the radial outer end of the tire 2. The double-headed arrow H is the radial distance from the bead baseline to this equatorial PE. In the JATTA standard, this distance H is also referred to as "cross-sectional height".

In FIG. 1, the reference numeral PW is a specific position on the outer surface of the tire 2. The tire 2 shows the maximum axial width at this position PW. This position PW is the maximum width position of the tire 2. This maximum axial width is also referred to as "cross-sectional width" in the JATTA standard. When the outer surface of the tire 2 is provided with irregularities such as grooves and dimples, the above-mentioned position PW is determined based on the virtual outer surface obtained assuming that there are no irregularities, that is, the profile. Be done. In the present invention, the tire 2 is incorporated into the rim R, the tire 2 is filled with air so as to have a normal internal pressure, and the outer surface of the tire 2 is a profile in a state where no load is applied to the tire 2. It is used as a base.

In FIG. 1, the double-headed arrow HWX is the radial distance from the bead baseline to the maximum width position PW. In this tire, the ratio of the distance HWX to the cross-sectional height H is set in the range of 0.3 to 0.6. In other words, for this tire, this ratio is 0.3 or more and 0.6 or less.

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a pair of support layers 14, a belt 16, a band 18, an inner liner 20, a pair of chafers 22 and a pair. The buffer layer 24 is provided. The tire 2 is composed of a large number of parts. This tire 2 is a tubeless type. The tire 2 is mounted on a passenger car.

The tread 4 has a shape that is convex outward in the radial direction. The tread 4 forms a tread surface 26 that is in contact with the road surface. A groove 28 is carved in the tread 4. A tread pattern is formed by the groove 28. The tread 4 has a base layer 30 and a cap layer 32. The cap layer 32 is laminated on the base layer 30. The base layer 30 is made of crosslinked rubber having excellent adhesiveness. The cap layer 32 is made of crosslinked rubber having excellent wear resistance, heat resistance and grip.

Each sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The radial outer portion of the sidewall 6 is joined to the tread 4. The radial inner portion of the sidewall 6 is joined to the clinch 8. The sidewall 6 is made of crosslinked rubber having excellent cut resistance and weather resistance.

Each clinch 8 extends substantially inward in the radial direction from the edge of the sidewall 6. The clinch 8 is located outside the bead 10 and the carcass 12 in the axial direction. As shown in FIG. 1, the clinch 8 is located outside the buffer layer 24 in the axial direction. The clinch 8 is made of a crosslinked rubber having excellent wear resistance. The clinch 8 comes into contact with the rim R.

In this tire 2, the hardness Hc of the clinch 8 is preferably 60 or more and 90 or less. When the hardness Hc is set to 60 or more, the clinch 8 contributes to the rigidity. In this tire 2, deformation of the bead 10 portion is suppressed. From this viewpoint, the hardness Hc is more preferably 65 or more. By setting this hardness Hc to 90 or less, the influence of the clinch 8 on the rigidity is suppressed. This tire 2 is excellent in riding comfort. From this viewpoint, the hardness Hc is more preferably 85 or less.

In the present invention, the hardness of each part constituting the tire 2 is measured by a type A durometer according to the provisions of "JIS K6253". The durometer is pressed against the cross section shown in FIG. 1 and the hardness is measured. The measurement is made at a temperature of 70 ° C. In the present invention, the hardness measured at a temperature of 70 ° C. is expressed as "hardness".

In this tire 2, the loss tangent (tan δ) Tc of the clinch 8 is preferably 0.08 or less. As a result, heat generation of the clinch 8 due to repeated deformation of the tire 2 is suppressed. The clinch 8 contributes to the durability of the tire 2. From this viewpoint, the loss tangent Tc is more preferably 0.07 or less, and more preferably 0.06 or less. Since the smaller the loss tangent Tc is, the more preferable it is, the preferable lower limit of the loss tangent Tc is not set.

In the present invention, the loss tangent (tan δ) of each part constituting the tire 2 is measured in accordance with the provisions of “JIS K 6394”. The measurement conditions are as follows. The measurement temperature of the loss tangent is 70 ° C. In the present invention, the loss tangent measured at a temperature of 70 ° C. is expressed as "loss tangent".
Viscoelastic spectrometer: "VESF-3" from Iwamoto Seisakusho
Initial distortion: 10%
Dynamic distortion: ± 1%
Frequency: 10Hz
Deformation mode: Tensile measurement temperature: 70 ° C

In FIG. 1, the double-headed arrow HC is the radial distance from the bead baseline to the radial outer end 34 of the clinch 8.

In the tire 2, the outer end 34 of the clinch 8 is located inside the maximum width position PW of the tire 2 in the radial direction. In other words, the ratio of distance HC to distance HWX is less than 100%. With this tire 2, the influence of the clinch 8 on the riding comfort is effectively suppressed. From this point of view, this ratio is preferably 90% or less, more preferably 85% or less. From the viewpoint that the clinch 8 effectively contributes to the rigidity, this ratio is preferably 50% or more, more preferably 55% or more.

Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 36 and an apex 38. The core 36 is ring-shaped and includes a wound non-stretchable wire. A typical material for wire is steel. The apex 38 extends substantially outward in the radial direction from the core 36. The apex 38 is tapered outward in the radial direction. In this tire 2, the apex 38 is located outside the core 36 in the radial direction. The bead 10 may be configured such that the apex 38 covers the core 36 in the radial inner portion of the bead 10.

In this tire 2, the Apex 38 is made of a high hardness crosslinked rubber. The apex 38 contributes to the rigidity of the portion of the bead 10.

In this tire 2, the hardness Ha of Apex 38 is preferably 70 or more and 95 or less. By setting this hardness Ha to 70 or more, Apex 38 contributes to rigidity. In this tire 2, deformation of the bead 10 portion is suppressed. From this viewpoint, the hardness Ha is more preferably 75 or more. By setting this hardness Ha to 95 or less, the influence of Apex 38 on the rigidity is suppressed. With this tire 2, a good ride quality is maintained. From this viewpoint, the hardness Ha is more preferably 90 or less. The hardness Ha of the apex 38 is measured in the same manner as the hardness Hc of the clinch 8 described above.

In this tire 2, the loss tangent Ta of Apex 38 is preferably 0.08 or less. As a result, heat generation of the Apex 38 due to repeated deformation of the tire 2 is suppressed. The apex 38 contributes to the durability of the tire 2. From this viewpoint, the loss tangent Ta is more preferably 0.07 or less, and more preferably 0.06 or less. Since the smaller the loss tangent Ta is, the more preferable it is, the preferable lower limit of the loss tangent Ta is not set. This loss tangent Ta is measured in the same manner as the loss tangent Tc of the clinch 8 described above.

In FIG. 1, reference numeral PA is the radial outer end of Apex 38. Reference numeral PB is the axial center of the bottom of Apex 38. The double-headed arrow LA represents the length of the line segment connecting the outer end PA and the center PB. The length LA is the length of the Apex 38.

In this tire 2, the outer end PA of the apex 38 is located inside the outer end 34 of the clinch 8 in the radial direction. In particular, in this tire 2, the length LA of the Apex 38 is 20 mm or less. In conventional tires, the apex has a length of 40 mm to 50 mm. This apex 38 is smaller than the conventional apex. If the apex 38 is too small, the rigidity of the bead 10 portion may be insufficient, and the steering stability may be impaired. From this point of view, the length LA is preferably 5 mm or more.

The carcass 12 includes a first carcass ply 40 and a second carcass ply 42. The carcass 12 is composed of two carcass plies. The carcass 12 may be formed from one carcass ply.

In this tire 2, the first carcass ply 40 (hereinafter, first ply) and the second carcass ply 42 (hereinafter, second ply) are bridged between the beads 10 on both sides, and the tread 4 and the sidewall are provided. Along with 6. The first ply 40 is folded back from the inside to the outside in the axial direction around each core 36. Due to this folding, a main portion 40a and a pair of folding portions 40b are formed on the first ply 40. The second ply 42 is folded back from the inside to the outside in the axial direction around each core 36. Due to this folding, a main portion 42a and a pair of folding portions 42b are formed on the second ply 42.

In the tire 12, the main portion 40a of the first ply 40 is located inside the main portion 42a of the second ply 42. The folded-back portion 40b of the first ply 40 is located outside the folded-back portion 42b of the second ply 42. The end of the folded portion 40b of the first ply 40 is located outside the end of the folded portion 42b of the second ply 42 in the radial direction. The end of the folded portion 40b of the first ply 40 may be located inside the end of the folded portion 42b of the second ply 42 in the radial direction.

In the tire 2, the end of the folded-back portion 40b of the first ply 40 is located near the position PW where the tire 2 shows the maximum width in the radial direction, and more specifically, outside the position PW. The carcass 12 has a "high turn-up structure (HTU)". In the tire 2, the carcass 12 is configured so that the end of the folded-back portion 40b extends directly below the end of the belt 16, in other words, the folded-back portion 40b overlaps the end portion of the belt 16. May be good. Such a structure of the carcass 12 is also referred to as an "ultra-high turn-up structure (U-HTU)".

Although not shown, each carcass ply consists of a number of parallel cords and topping rubber. The absolute value of the angle each code makes with respect to the equatorial plane is 75 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord consists of organic fibers. Preferred organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

Each support layer 14 is located axially inside the sidewall 6. The support layer 14 is located axially inside the carcass 12. The support layer 14 is sandwiched between the carcass 12 and the inner liner 20. The support layer 14 is tapered inward and tapered outward in the radial direction. The support layer 14 has a shape similar to that of a crescent moon. In the tire 2, the radial outer end portion of the support layer 14 overlaps the end portion of the belt 16. The portion of the support layer 14 at the inner end in the radial direction overlaps with the portion of the apex 38 of the bead 10.

The support layer 14 is made of crosslinked rubber. When the tire 2 punctures, the support layer 14 supports the load. With this support layer 14, the tire 2 can travel a certain distance even in a punctured state. This tire 2 is also called a run-flat tire. This tire 2 is a side reinforcement type.

From the viewpoint of suppressing vertical bending in a punctured state, the hardness Hi of the support layer 14 is preferably 60 or more, more preferably 65 or more. From the viewpoint of riding comfort in a state where the internal pressure is maintained, that is, in a normal state, the hardness Hi is preferably 85 or less, more preferably 80 or less. The hardness Hi of the support layer 14 is measured in the same manner as the hardness Hc of the clinch 8 described above.

In this tire 2, the loss tangent Ti of the support layer 14 is preferably 0.07 or less. As a result, heat generation of the support layer 14 due to repeated deformation of the tire 2 is suppressed. The support layer 14 contributes to the durability of the tire 2. From this viewpoint, the loss tangent Ti is more preferably 0.05 or less, and more preferably 0.04 or less. Since the smaller the loss tangent Ti is, the more preferable it is, the preferable lower limit of the loss tangent Ti is not set. This loss tangent Ti is measured in the same manner as the loss tangent Tc of the clinch 8 described above.

The belt 16 is located inside the tread 4 in the radial direction. The belt 16 is laminated with the carcass 12. The belt 16 reinforces the carcass 12. The belt 16 is composed of an inner layer 44 and an outer layer 46. The belt 16 may include three or more layers. Although not shown, each of the inner layer 44 and the outer layer 46 consists of a number of parallel cords and topping rubbers. Each cord is inclined with respect to the equatorial plane. The general absolute value of the tilt angle is 10 ° or more and 35 ° or less. The direction of inclination of the cord of the inner layer 44 with respect to the equatorial plane is opposite to the direction of inclination of the cord of the outer layer 46 with respect to the equatorial plane. The preferred material for the cord is steel. Organic fibers may be used for the cord.

In the tire 2, the axial width of the belt 16 is preferably 0.6 times or more the maximum width of the tire 2 from the viewpoint of reinforcing the carcass 12 by the belt 16. From the viewpoint of the influence on durability, the axial width of the belt 16 is preferably 0.9 times or less the maximum width of the tire 2.

The band 18 is located on the outer side in the radial direction of the belt 16. Although not shown, the band 18 consists 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 preferably 5 ° or less, more preferably 2 ° or less. Since the belt 16 is restrained by this cord, the lifting of the belt 16 is suppressed. The cord consists of organic fibers. Preferred organic fibers include nylon fibers, polyester fibers, rayon fibers, polyethylene naphthalate fibers and aramid fibers.

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

The inner liner 20 is located inside the carcass 12. Inside the tread 4 in the radial direction, the inner liner 20 is joined to the inner surface of the carcass 12. Inside the sidewall 6 in the axial direction, the inner liner 20 is joined to the inner surface of the support layer 14. The inner liner 20 is made of crosslinked rubber having excellent air shielding properties. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 2.

Each chafer 22 is located in the vicinity of the bead 10. When the tire 2 is incorporated into the rim R, the chafer 22 comes into contact with the rim R. This contact protects the vicinity of the bead 10. In this embodiment, the chafer 22 is integral with the clinch 8. Therefore, the material of the chafer 22 is the same as that of the clinch 8. The chafer 22 may consist of a cloth and rubber impregnated in the cloth.

Each buffer layer 24 is located between the carcass 12 and the clinch 8 in the axial direction. As is clear from FIG. 1, the buffer layer 24 extends substantially outward in the radial direction along the carcass 12 from the vicinity of the core 36.

In this tire 2, the crosslinked rubber having the hardness Hk and the loss tangent Tk adjusted as follows with respect to the loss tangent Tc of the clinch 8 and the hardness Ha and the loss tangent Ta of the apex 38 cushions the tire 2. It is adopted in the layer 24. The hardness Hk is measured in the same manner as the hardness Hc of the clinch 8 described above. This loss tangent Tk is measured in the same manner as the loss tangent Tc of the clinch 8 described above.

In this tire 2, the loss tangent Tk of the buffer layer 24 is equal to or less than the loss tangent Tc of the clinch 8 and the loss tangent Ta of the apex 38. The hardness Hk of the buffer layer 24 is equal to or higher than the hardness Ha of the apex 38. The buffer layer 24 is made of a crosslinked rubber that is less likely to generate heat than the crosslinked rubber of the clinch 8 and the crosslinked rubber of the Apex 38 and has a rigidity equal to or higher than the rigidity of the crosslinked rubber of the Apex 38. In this tire 2, the buffer layer 24 is hard and does not easily generate heat.

FIG. 2 shows the portion of the bead 10 of the tire 2 shown in FIG. In FIG. 2, the vertical direction is the radial direction of the tire 2, the left-right 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. 2, reference numeral P1 represents a specific position on the outer surface of the tire 2. In this tire 2, the height in the radial direction from the bead baseline to this position P1 is 14 mm. This position P1 is a position on the outer surface of the tire 2 where the height in the radial direction from the bead baseline is 14 mm. In the present invention, this position P1 is referred to as a first point. The reference numeral P2 represents a specific position on the outer surface of the tire 2 as well as the position P1. In this tire 2, the height in the radial direction from the bead baseline to this position P2 is 20 mm. This position P2 is a position on the outer surface of the tire 2 where the height in the radial direction from the bead baseline is 20 mm. In the present invention, this position P2 is referred to as a second point.

In the present invention, at the first point P1 and the second point P2, the tire 2 is incorporated in the rim R, the tire 2 is filled with air so as to have a normal internal pressure, and the tire 2 is not loaded. It is determined by the profile based on the outer surface of the obtained tire 2.

In FIG. 2, the solid line L1 is a straight line extending in the radial direction through the first point P1. The solid line L2 is a straight line extending in the radial direction through the second point P2.

In this tire 2, the buffer layer 24 overlaps each of the first point P1 and the second point P2 in the radial direction. The buffer layer 24 overlaps the zone from the first point P1 to the second point P2 in the radial direction. The buffer layer 24 bridges the straight line L1 and the straight line L2.

In the manufacture of the tire 2, a plurality of rubber members are assembled to obtain a low cover (unvulcanized tire 2). This low cover is put into the mold. The outer surface of the low cover is in contact with the cavity surface of the mold. The inner surface of the low cover abuts on the bladder or core. The low cover is pressurized and heated in the mold. The low cover rubber composition flows by pressurization and heating. The rubber undergoes a cross-linking reaction by heating, and the tire 2 is obtained. By using a mold having an uneven pattern on the cavity surface, an uneven pattern is formed on the tire 2.

The tire 2 is used by being fitted to the rim R. In this usage state, the bead 10 portion of the tire 2 comes into contact with the rim R. As a result, a contact surface is formed between the tire 2 and the rim R.

In the tire 2, the zone from the first point P1 to the second point P2 corresponds to the radial outer portion of the contact surface. Inside the radial direction from this portion, the tire 2 is firmly fixed to the rim R. On the outer side in the radial direction from this portion, the tire 2 is released from the rim R. Therefore, distortion tends to concentrate near this portion. When the tire 2 punctures and the internal pressure drops, the tire 2 itself supports the vehicle weight. At this time, a large load is applied to the tire 2. Therefore, when the tire 2 is punctured and the internal pressure is lowered, that is, in the run-flat running, a large load is applied to the bead 10 portion of the tire 2, and the strain tends to be particularly concentrated.

In this tire 2, a small apex 38 is adopted. In the tire 2, the apex 38 is arranged outside the region where the strain is concentrated in the punctured state. With this tire 2, the deformation of the Apex 38 is effectively suppressed in the run-flat running. The apex 38 contributes to the prevention of damage at the bead 10.

In this tire 2, as described above, a buffer layer 24 is provided between the carcass 12 and the clinch 8.

In this tire 2, as described above, the buffer layer 24 overlaps the zone from the first point P1 to the second point P2 in the radial direction. In the tire 2, the cushioning layer 24 is arranged so as to cover a portion where the tire 2 and the rim R are in contact with each other in a state where the tire 2 is combined with the rim R. In the tire 2, the cushioning layer 24 is provided in a portion where strain is likely to be concentrated in the run-flat running. Since the buffer layer 24 is hard and does not easily generate heat, damage to the bead 10 portion is effectively suppressed in the tire 2.

In FIG. 1, the double-headed arrow HKS represents the radial distance from the bead baseline to the radial outer end 48 of the buffer layer 24. The double-headed arrow HKU represents the radial distance from the bead baseline to the radial inner end 50 of the buffer layer 24. The double-headed arrow HB represents the radial distance from the bead baseline to the radial outer end 52 of the core 36.

In the tire 2, the outer end 48 of the cushioning layer 24 is located radially inside the maximum width position PW of the tire 2. Specifically, the ratio of the distance HKS to the distance HWX is less than 100%. As a result, the concentration of strain on the outer end 52 is suppressed, and heat generation at the outer end 48 of the buffer layer 24 is effectively suppressed. The tire 12 has excellent durability. Since the volume of the buffer layer 24 is properly maintained, the influence of the buffer layer 24 on the mass and rolling resistance is suppressed. From this point of view, this ratio is preferably 90% or less, more preferably 85% or less. From the viewpoint that the buffer layer 24 effectively contributes to the rigidity of the portion of the bead 10, this ratio is preferably 50% or more, more preferably 55% or more.

In this tire 2, the outer end 48 of the cushioning layer 24 is located near the outer end 34 of the clinch 8 in the radial direction. Specifically, in this tire 2, the ratio of the distance HKS to the radial distance HC from the bead baseline to the outer end 34 of the clinch 8 is 85% or more and 105% or less. By setting this ratio to 85% or more, the volume of the buffer layer 24 is sufficiently secured. The buffer layer 24 effectively contributes to the suppression of deformation and heat generation of the portion of the bead 10. With this tire 2, durability in good run-flat running is maintained, and rolling resistance is effectively reduced. By setting this ratio to 105% or less, the buffer layer 24 is prevented from protruding significantly from the clinch 8 in the radial direction. In the tire 2, the concentration of strain on the outer end 48 of the buffer layer 24 is suppressed, and the volume of the buffer layer 24 is appropriately maintained. In the tire 2, the influence of the buffer layer 24 on the rolling resistance and the mass is suppressed, and the durability in good run-flat running is maintained.

In the tire 2, the position of the inner end 50 of the buffer layer 24 coincides with the position of the outer end 52 of the core 36 in the radial direction, or the inner end 50 of the buffer layer 24 is the outer end 52 of the core 36. It is located outside. In other words, the ratio of the distance HKU to the distance HB is 100% or more. In this tire 2, the cushioning layer 24 does not overlap with the core 36 in the axial direction. The axially outer portion of the core 36 is composed of a clinch 8 except for the carcass 12. Since the hard buffer layer 24 is not arranged between the core 36 and the clinch 8, the volume of the clinch 8 is sufficiently secured. With this tire 2, the clinch 8 is hard to wear. In the tire 2, the position of the core 36 with respect to the rim R is stably maintained in the running state. Since the core 36 is difficult to move with respect to the rim R, the deformation of the bead 10 portion is effectively suppressed in this tire 2. Since heat generation is suppressed, durability can be further improved. From this point of view, this ratio is preferably 105% or more. When the inner end 50 of the buffer layer 24 is separated from the core 36 outward in the radial direction, the volume of the buffer layer 24 becomes smaller, and the heat generation suppressing effect of the buffer layer 24 may be diminished. From the viewpoint of exerting the heat generation suppressing effect by the buffer layer 24, this ratio is preferably 150% or less, more preferably 145% or less.

As described above, in the tire 2, the cushioning layer 24, which is hard and does not easily generate heat, is arranged at an appropriate position and in an appropriate size in consideration of a region where strain is concentrated. The hard buffer layer 24 suppresses deformation of the bead 10 portion not only during normal running but also when the internal pressure is lowered due to a puncture. In this tire 2, heat generation due to deformation of the bead 10 portion is effectively suppressed. In particular, in this tire 2, heat generation between the contact surface with the rim R and the carcass 12 is suppressed. In the tire 2, since the cushioning layer 24 itself does not easily generate heat, heat generation is considerably effectively suppressed in the portion of the bead 10. In this tire 2, the occurrence of damage at the bead 10 portion is effectively suppressed.

Further, in the tire 2, the cushioning layer 24 arranges the carcass 12, particularly the folded-back portion 40b of the first ply 40, axially inward from the folded-back portion of the conventional tire in which the buffer layer 24 is not provided. More specifically, due to the adoption of the buffer layer 24, the folded-back portion 40b of the first ply 40 has the bead 10 of the tire 2 in the region from the straight line L1 to the straight line L2 as shown in FIG. It is placed approximately in the center of the part. In this tire 2, it is prevented that a force in the compression direction or the tension direction acts on the carcass 12, more specifically, the folded-back portion 40b of the first ply 40. Distortion is less likely to concentrate on the carcass 12. With this tire 2, the carcass 12 is unlikely to be damaged. In this tire 2, the occurrence of damage at the bead 10 portion is effectively suppressed.

In this tire 2, a small apex 38 is adopted, and by arranging a hard and heat-generating buffer layer 24 at an appropriate position and an appropriate size, running in a state where the internal pressure is lowered due to a puncture, that is, In the run-flat run, damage to the bead 10 portion is effectively suppressed. With this tire 2, a sufficient mileage is secured even when the internal pressure is lowered due to a flat tire. The tire 2 has excellent durability in run-flat running.

In this tire 2, the synergistic action of the apex 38 and the cushioning layer 24 suppresses the occurrence of damage at the bead 10, so that the volume of the support layer 14 can be reduced. The reduction in the volume of the support layer 14 contributes to the weight reduction of the tire 2 and the reduction of rolling resistance. With this tire 2, weight reduction and reduction of rolling resistance can be achieved while improving durability in run-flat running. According to the present invention, it is possible to obtain a pneumatic tire 2 in consideration of weight reduction and reduction of rolling resistance while improving durability in run-flat running.

In the tire 2, the heat generation of the buffer layer 24 is about the same as the heat generation of the clinch 8, or the heat generation of the buffer layer 24 is less likely to be generated than that of the clinch 8. Specifically, the difference (Tc-Tk) between the loss tangent Tc of the clinch 8 and the loss tangent Tk of the buffer layer 24 is preferably 0.00 or more. As a result, the buffer layer 24 effectively contributes to the suppression of heat generation due to the deformation of the bead 10. The tire 2 has excellent durability in run-flat running. From this point of view, this difference is more preferably 0.01 or more, and even more preferably 0.02 or more. Since it is preferable that the loss tangent Tk is smaller than the loss tangent Tc, the upper limit of this difference is not set.

In the tire 2, the heat generation of the buffer layer 24 is about the same as the heat generation of the Apex 38, or the heat generation of the buffer layer 24 is less likely to be generated than that of the Apex 38. Specifically, the difference (Ta-Tk) between the loss tangent Ta of the Apex 38 and the loss tangent Tk of the buffer layer 24 is preferably 0.00 or more. As a result, the buffer layer 24 effectively contributes to the suppression of heat generation due to the deformation of the bead 10. The tire 2 has excellent durability in run-flat running. From this point of view, the difference is more preferably 0.01 or more, and even more preferably 0.02 or more. Since it is preferable that the loss tangent Tk is smaller than the loss tangent Ta, the upper limit of this difference is not set.

In this tire 2, the loss tangent Tk of the buffer layer 24 is preferably 0.06 or less. As a result, the buffer layer 24 effectively contributes to the suppression of heat generation due to the deformation of the bead 10. The tire 2 has excellent durability in run-flat running. From this viewpoint, the loss tangent Tk is more preferably 0.05 or less, and further preferably 0.04 or less. Since the smaller the loss tangent Tk is, the more preferable it is, the preferable lower limit of the loss tangent Tk is not set.

In this tire 2, preferably, the loss tangent Tk of the buffer layer 24 is equal to or less than the loss tangent Ti of the support layer 14. In other words, the difference (Ti−Tk) between the loss tangent Ti of the support layer 14 and the loss tangent Tk of the buffer layer 24 is preferably 0.00 or more. As a result, the heat generation suppressing effect of the buffer layer 24 is further enhanced. The tire 2 is more excellent in durability in run-flat running. From this point of view, this difference is more preferably 0.01 or more. Since it is preferable that the loss tangent Tk is smaller than the loss tangent Ti, the upper limit of this difference is not set.

In this tire 2, it is more preferable that the loss tangent Tk of the buffer layer 24 is lower than the loss tangent Tc of the clinch 8 and the loss tangent Ta of the apex 38. In this tire 2, the loss tangent Tk of the buffer layer 24 is equal to or less than the loss tangent Ti of the support layer 14, and more preferably lower than the loss tangent Tc of the clinch 8 and the loss tangent Ta of the apex 38. As a result, the rigidity balance of the entire tire is appropriately adjusted, and not only the durability in the run-flat running but also the steering stability and the riding comfort in the normal running are improved.

In the tire 2, the rigidity of the cushioning layer 24 is about the same as the rigidity of the apex 38, or the cushioning layer 24 is harder than the apex 38. Specifically, the difference (Hk-Ha) between the hardness Hk of the buffer layer 24 and the hardness Ha of the apex 38 is preferably 0 or more. As a result, the buffer layer 24 contributes to the suppression of deformation of the bead 10 portion not only during normal running but also during run-flat running. In this tire 2, damage to the portion of the bead 10 is effectively suppressed. From this point of view, the difference is more preferably 5 or more. From the viewpoint of preventing the concentration of strain due to the difference in rigidity between the cushioning layer 24 and the apex 38, this difference is preferably 20 or less.

In this tire 2, the hardness Hk of the buffer layer 24 is preferably 60 or more and 95 or less. When the hardness Hk is set to 60 or more, the buffer layer 24 has appropriate rigidity. In this tire 2, the degree of deformation of the portion of the bead 10 is appropriately maintained. From this viewpoint, the hardness Hk is more preferably 65 or more. By setting this hardness Hk to 95 or less, the rigidity of the buffer layer 24 is appropriately maintained. With this tire 2, a good ride quality is maintained. From this viewpoint, the hardness Hk is more preferably 90 or less.

In the tire 2, preferably, the hardness Hk of the buffer layer 24 is equal to or higher than the hardness Hi of the support layer 14. In other words, the difference (Hk-Hi) between the hardness Hk of the buffer layer 24 and the hardness Hi of the support layer 14 is preferably 0 or more. As a result, the buffer layer 24 contributes to the suppression of deformation of the bead 10 portion not only during normal running but also during run-flat running. In this tire 2, damage to the portion of the bead 10 is effectively suppressed. From this point of view, this difference is more preferably 5 or more, and even more preferably 10 or more. From the viewpoint of preventing the concentration of strain due to the difference in rigidity between the cushioning layer 24 and the support layer 14, this difference is preferably 30 or less.

In this tire 2, the hardness Hk of the buffer layer 24 is equal to or higher than the hardness Ha of the apex 38, and more preferably larger than the hardness Hi of the support layer 14. As a result, the rigidity balance of the entire tire is appropriately adjusted, and not only the durability in the run-flat running but also the steering stability and the riding comfort in the normal running are improved.

In FIG. 2, the solid line LT is the normal line of the outer surface of the tire 2. This normal LT passes through the second reference point P2. In the present invention, the normal LT of the outer surface of the tire 2 at the second reference point P2 is referred to as a reference normal.

In FIG. 2, the double-headed arrow t represents the length from the outer surface of the tire 2 to the carcass 12. This length t is the thickness of the outer portion of the carcass 12 of the tire 2 at the second reference point P2. The double-headed arrow tk is the thickness of the buffer layer 24 at the second reference point P2. The double-headed arrow tc is the thickness of the clinch 8 at the second reference point P2. The thickness t, thickness tk and thickness tk are measured along the reference normal LT. The thickness t is equal to the sum of the thickness tk and the thickness tk (tk + tk). This thickness t is the total thickness of the thickness tk of the buffer layer 24 and the thickness tk of the clinch 8 measured along the reference normal LT. The double-headed arrow tL is the thickness of the support layer 14 measured along this reference normal LT.

In this tire 2, the thickness tk of the buffer layer 24 is preferably 1 mm or more. When the thickness tk is set to 1 mm or more, the buffer layer 24 effectively contributes to the suppression of heat generation in the portion of the bead 10. From this viewpoint, the thickness tk is more preferably 2 mm or more. The thickness tk is preferably 6 mm or less. By setting this thickness tk to 6 mm or less, the influence of the buffer layer 24 on the rigidity of the portion of the bead 10 is suppressed. In this tire 2, the rigidity of the portion of the bead 10 is appropriately maintained. From this viewpoint, the thickness tk is more preferably 5 mm or less.

In this tire 2, the thickness tc of the clinch 8 is preferably 1 mm or more. By setting this thickness tc to 1 mm or more, the rigidity of the clinch 8 is appropriately maintained. In the tire 2, the clinch 8 effectively prevents the portion of the bead 10 from being worn by contact with the rim R. The tire 2 has excellent wear resistance. From this viewpoint, the thickness tc is more preferably 2 mm or more. The thickness tc is preferably 6 mm or less. By setting this thickness tc to 6 mm or less, the influence of the clinch 8 on the rigidity of the portion of the bead 10 is suppressed. In this tire 2, the rigidity of the portion of the bead 10 is appropriately maintained. From this viewpoint, the thickness tc is more preferably 5 mm or less.

In this tire 2, the ratio of the thickness tk to the total thickness t is preferably 15% or more and 85% or less. When this ratio is set to 15% or more, the buffer layer 24 effectively contributes to the suppression of heat generation in the portion of the bead 10. By setting this ratio to 85% or less, the influence of the buffer layer 24 on the rigidity of the portion of the bead 10 is suppressed. In this tire 2, the rigidity of the portion of the bead 10 is appropriately maintained.

In this tire 2, the ratio of the total thickness t to the thickness tL is preferably 80% or more and 120% or less. By setting this ratio to 80% or more, the balance between the thickness of the outer portion of the carcass 12 and the thickness of the load supporting layer 14 is adjusted, and the force in the compression direction is prevented from acting on the carcass 12. .. Since the carcass 12 is prevented from being damaged, the tire 2 has excellent durability. By setting this ratio to 120% or less, the balance between the thickness of the outer portion of the carcass 12 and the thickness of the support layer 14 is adjusted, and the force in the tensile direction is prevented from acting on the carcass 12. Even in this case, the carcass 12 is prevented from being damaged, so that the tire 2 has excellent durability.

In this tire 2, the sum (tk + tk + tL) of the thickness tk of the buffer layer 24, the thickness tk of the clinch 8 and the thickness tL of the support layer 14 is preferably less than 18 mm. In this tire 2, the portion of the bead 10 has a small thickness. In this tire 2, weight reduction and rolling resistance can be reduced. From this point of view, the sum (tk + tk + tL) is more preferably 17 mm or less. The sum (tk + tk + tL) is preferably 10 mm or more from the viewpoint that the rigidity of the portion of the bead 10 is appropriately maintained and the durability in run-flat running is improved.

In FIG. 2, the double-headed arrow ti represents the thickness of the support layer 14. This thickness ti is measured along a straight line extending in the axial direction through the position PW. In the present invention, this thickness ti is the thickness of the support layer 14 at the maximum width position PW of the tire 2.

In the tire 2, the thickness ti of the support layer 14 is preferably 6 mm or more from the viewpoint that the support layer 14 contributes to the support of the load when the tire 2 is punctured. From the viewpoint of riding comfort in a normal state, the thickness ti of the support layer 14 is preferably 15 mm or less.

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

[Example 1]
The tire shown in Fig. 1-2 was manufactured. The size of this tire is 245/45 RF19. The specifications of this Example 1 are as shown in Table 1 below.

The buffer layer is arranged so as to overlap the zone from the first point P1 to the second point P2 in the radial direction. This is indicated by "Y" in the columns of the first point (14 mm) and the second point (20 mm) in the table.

The loss tangent Tk and hardness Hk of the buffer layer in Table 1 are measured at a temperature of 70 ° C. The clinch loss tangent Tc measured at a temperature of 70 ° C. was 0.06. The clinch hardness Hc measured at a temperature of 70 ° C. was 75. The loss tangent Ta of Apex measured at a temperature of 70 ° C. was 0.06. The hardness Ha of Apex measured at a temperature of 70 ° C. was 80. The loss tangent Ti of the support layer measured at a temperature of 70 ° C. was 0.04. The hardness Hi of the support layer measured at a temperature of 70 ° C. was 70.

[Comparative Example 1]
A buffer layer having a loss tangent Tk and a hardness Hk shown in Table 1 below was used, and this buffer layer was arranged axially inward from the zone from the first point P1 to the second point P2. A tire of Comparative Example 1 was obtained in the same manner as in Example 1. In Comparative Example 1, the buffer layer does not overlap the first point P1 and the second point P2 in the radial direction. This is represented by "N" in the columns of the first point (14 mm) and the second point (20 mm) in Table 1. The specifications of this Comparative Example 1 are as shown in Table 1 below. In this Comparative Example 1, since the normal LT also intersects the apex, the total of the thickness tL and the thickness of the apex is described in the column of "thickness tL" in Table 1.

[Comparative Example 2]
A buffer layer having a loss tangent Tk and a hardness Hk shown in Table 1 below was used, and this buffer layer was arranged axially outside the zone from the first point P1 to the second point P2. A tire of Comparative Example 2 was obtained in the same manner as in Example 1. In Comparative Example 2, as in Comparative Example 1, the buffer layer does not overlap with the first point P1 and the second point P2 in the radial direction. This is represented by "N" in the columns of the first point (14 mm) and the second point (20 mm) in Table 1. The specifications of this Comparative Example 2 are as shown in Table 1 below. In Comparative Example 2, as in Comparative Example 1 described above, the normal LT also intersects with Apex. Therefore, in the “Thickness tL” column of Table 1, the sum of the thickness tL and the thickness of Apex is displayed. Is described.

[Example 2]
By changing the loss tangent Tk of the buffer layer, the difference between the loss tangent Tc and the loss tangent Tk (Tc-Tk), the difference between the loss tangent Ta and the loss tangent Tk (Ta-Tk), and the loss tangent Ti and the loss tangent Tk The tires of Example 2 were obtained in the same manner as in Example 1 except that the difference (Ti-Tk) was as shown in Table 1 below.

[Example 3]
The tire of Example 3 was obtained in the same manner as in Example 2 except that the thickness tk of the buffer layer and the thickness tk of the clinch were set as shown in Table 1 below.

[Example 4]
The ratio ((tk + tk) / tL) was set as shown in Table 1 below by changing the thickness tk of the buffer layer, the thickness tk of the clinch, and the thickness tL of the support layer, and the same as in Example 2. The tire of Example 4 was obtained.

[Durability (run flat)]
A tire was incorporated into a rim (size = 19 × 8J), and the tire was filled with air to set an internal pressure of 180 kPa. This tire was mounted on a drum type running tester, and a vertical load corresponding to 80% of the maximum load of the tire was applied to the tire. The punctured state was reproduced by setting the internal pressure of this tire as normal pressure (measured pressure is 0 kPa), and the tire was run at a speed of 80 km / h on a drum having a radius of 1.7 m. The mileage until the tire broke was measured. The results are shown in Table 1 below as indices. The larger the value, the better the run-flat durability, which is preferable.

[Rolling resistance coefficient (RRC)]
The rolling resistance coefficient (RRC) was measured under the following measurement conditions using a rolling resistance tester.
Rim used: 19 x 8J (made of aluminum alloy)
Internal pressure: 220 kPa
Load: 4.6kN
Speed: 80km / h
This result is an index expressed based on the reciprocal of the measured rolling resistance coefficient, and is shown in Table 1 below. The larger the value, the more the rolling resistance is reduced, which is preferable.

[mass]
The mass of the tire was measured. This result is an exponent expressed based on the reciprocal of the measured mass and is shown in Table 1 below. The larger the value, the lighter the weight, which is preferable.

As shown in Table 1, the tires of the examples have a higher evaluation than the tires of the comparative examples. From this evaluation result, the superiority of the present invention is clear.

The techniques relating to the buffer layer described above can also be applied to various tires.

2 ... Tires 4 ... Treads 6 ... Sidewalls 8 ... Clinch 10 ... Beads 12 ... Carcass 14 ... Support layer 24 ... Buffer layer 34 ... Clinch 8 Radial outer end 36 ... Core 38 ... Apex 40 ... First ply 40a ... Main part 40b ... Folded part 42 ... Second ply 42a ... Main part 42b ... -Folded portion 48 ... Radial outer end of the buffer layer 24 50 ... Radial inner end of the buffer layer 24 52 ... Radial outer end of the core 36

Claims (4)

It has a tread, a pair of sidewalls, a pair of clinches, a pair of beads, a carcass, a pair of support layers and a pair of cushioning layers.
Each sidewall extends substantially inward in the radial direction from the end of the tread.
Each clinch extends substantially inward in the radial direction from the edge of the sidewall.
Each bead is located axially inside the clinch above,
The carcass spans between one bead and the other along the inside of the tread and sidewalls.
Each support layer is located axially inside the sidewall and
Each buffer layer is located between the carcass and the clinch,
The bead has a core and an apex, and the apex extends substantially outward in the radial direction from the core, and the length of the apex is 20 mm or less.
The outer edge of the buffer layer is located radially inside the maximum width position of this tire.
In the radial direction, the position of the inner edge of the buffer layer coincides with the position of the outer edge of the core, or the inner edge of the buffer layer is located outside the outer edge of the core.
The ratio of the radial distance from the bead baseline to the outer edge of the buffer layer to the radial distance from the bead baseline to the outer edge of the clinch is 85% or more and 105% or less.
When the position on the outer surface of the tire where the radial height from the bead baseline is 14 mm is the first point P1 and the position where the radial height from the bead baseline is 20 mm is the second point P2. In the radial direction, the buffer layer overlaps with each of the first point P1 and the second point P2.
The loss tangent of the buffer layer is equal to or less than the loss tangent of the clinch and the loss tangent of the apex.
A pneumatic tire in which the hardness of the buffer layer is equal to or higher than the hardness of the apex. The pneumatic tire according to claim 1, wherein the loss tangent of the buffer layer is equal to or less than the loss tangent of the support layer. When the normal of the outer surface of the tire at the second point P2 is used as the reference normal, the thickness of each of the buffer layer and the clinch measured along the reference normal is 1 mm or more. The pneumatic tire according to Item 1 or 2. The ratio of the total thickness of the buffer layer thickness and the clinch thickness measured along the reference normal to the thickness of the support layer measured along the reference normal is 80% or more. The pneumatic tire according to claim 3, which is 120% or less.

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