tire

Abstract

To provide a tire 2 which can be improved in durability without being accompanied by mass increase.SOLUTION: A tire 2 comprises a pair of beads 8, a carcass 10, a pair of side wall layers 6, and a belt 12. One carcass ply 40 constituting the carcass 10 comprises a ply main body 42 and a pair of folded-back portions 44. Height in a radial direction of the folded-back portions 44 is below 17% of height of a cross section. An average height F of a side wall layer 3 in a zone ZF satisfies the following formula (1) represented using a constant B as well as and width SW of a cross section of the tire 2 and a width BW of the belt 12: the formula (1): 416×(BW / SW-B)2+4≤F≤416×(BW / SW-B)2+6. The constant B satisfies the following formula (2) represented using oblateness RA of the tire: the formula (2): B=0.84×(-0.49×RA / 100+1.22).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a tire. In particular, the present invention relates to a tire for use on a passenger vehicle. [Background technology]

[0002] The mass of a tire affects its rolling resistance. In light of environmental considerations, tires with low rolling resistance are in demand. In order to reduce the weight of the tire, the number of carcass plies constituting the carcass is reduced, the length of the turned-up portion of the carcass ply is shortened, etc., but this reduces the rigidity of the bead portion. A large load acts on the bead part of a tire. Moreover, the tire undergoes repeated deformation and recovery while in motion. There is concern that the bead part is easily damaged. There is a demand for improving the durability of the bead part. If a new element is incorporated into the bead portion in order to improve the durability of the bead portion, the mass of the tire will increase. Accordingly, various studies have been conducted to establish a technique capable of maintaining the durability of the bead portion while reducing the weight of the tire (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-286211 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can improve durability without increasing the mass. [Means for solving the problem]

[0005] A tire according to one embodiment of the present invention is a HIGH LOAD CAPACITY type tire defined in the ETRTO 2021 standard manual. This tire includes a pair of beads, a carcass spanning between the pair of beads, a pair of sidewall layers located axially outside the carcass, and a belt located radially outside the carcass. Each of the pair of beads includes a core and an apex located radially outside the core. The carcass is composed of one carcass ply. The carcass ply includes a ply body spanning between the pair of cores, and a pair of turn-up portions connected to the ply body and turned up at each of the cores. The radial height of the pair of turn-up portions is 17% or less of the cross-sectional height of the tire. The average thickness F of the sidewall layer in a zone from 20 mm to 30 mm in the radial direction from the bead base line satisfies the following formula (1), which is expressed using a constant B, and the tire cross-sectional width SW and belt width BW obtained in a reference state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire. The constant B satisfies the following formula (2) expressed using the aspect ratio RA of the tire. Formula (1): 416×(BW / SW-B) 2 +4≦F≦416×(BW / SW-B) 2 +6 Formula (2): B=0.84×(-0.49×RA / 100+1.22) Effect of the Invention

[0006] According to the present invention, a tire can be obtained that can improve durability without increasing the mass. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating a configuration of a belt. [Diagram 3]FIG. 4 is an enlarged cross-sectional view showing a bead portion. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a bead portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The tire of the present invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire mounted on the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire mounted on the rim.

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is called a standard state. The state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire is called the reference state.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in the meridian section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads is the same as the distance between the beads of the tire mounted on a regular rim. The tire configuration that cannot be confirmed when the tire is mounted on a regular rim is confirmed on the aforementioned cut surface.

[0011] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0012] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] In the present invention, unless otherwise specified, the load index (LI) is a load index for a HIGH LOAD CAPACITY type tire (hereinafter referred to as an HLC type tire) defined in the ETRTO 2021 standard manual, and is the maximum mass that can be loaded onto the tire under specified conditions, that is, the maximum load capacity. It is an index that represents the maximum load capacity.

[0015] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0016] [Foundations underlying the present invention] Due to environmental considerations, electric vehicles are becoming more popular. Electric vehicles are equipped with batteries. Batteries that allow a vehicle to travel a distance of around 500 km are heavy. Therefore, electric vehicles tend to be heavier than conventional gasoline-powered vehicles. Therefore, tires installed on electric vehicles are subjected to a higher load than tires installed on gasoline-powered vehicles. In order to provide a tire capable of supporting a high load, in the ETRTO standard, the load index has been reviewed, and tires of the HIGH LOAD CAPACITY type (hereinafter referred to as HLC type) have been introduced as a new category. To be applicable as an HLC type tire, it is required that the tire be able to support a higher load than before. To achieve this, the rigidity of the tire needs to be increased. However, when the rigidity of the tire is increased, there is a concern that the mass of the tire will increase as described above. Therefore, the inventor confirmed the ratio of the belt width to the cross-sectional width of the tire and the thickness of the sidewall layer in the bead portion, and found that the two are correlated. If the belt width is within an appropriate range with respect to the cross-sectional width of the tire, even if a carcass composed of a single carcass ply and having a turn-up structure is adopted, while imparting the required rigidity to the tire, it is possible to make the sidewall layer in the bead portion thinner, and thus the invention described below has been completed.

[0017] [Summary of Embodiments of the Present Invention] The present invention relates to a HIGH LOAD CAPACITY type tire defined in the ETRTO 2021 standard manual, comprising a pair of beads, a carcass spanning between the pair of beads, a pair of sidewall layers positioned axially outward of the carcass, and a belt positioned radially outward of the carcass, wherein each of the pair of beads comprises a core and an apex positioned radially outward of the core, the carcass being composed of one carcass ply, the carcass ply comprising a ply body spanning between the pair of cores, and a pair of turn-up portions connected to the ply body and turned up at each of the cores, and the pair of turn-up portions The tire has a radial height of a turned up portion that is 17% or less of the section height of the tire, and an average thickness F of the sidewall layer in a zone that is 20 mm to 30 mm radially from a bead base line satisfies the following formula (1) expressed using a constant B, and the section width SW of the tire and the belt width BW obtained in a reference state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire, and the constant B satisfies the following formula (2) expressed using the aspect ratio RA of the tire. Formula (1): 416×(BW / SW-B) 2 +4≦F≦416×(BW / SW-B) 2 +6 Formula (2): B=0.84×(-0.49×RA / 100+1.22)

[0018] The tire of the present invention can improve durability without increasing the mass. The mechanism by which such an effect is achieved has not been clarified, but is presumed to be as follows.

[0019] In a rolling tire, the surface portion of the zone ZF is repeatedly subjected to compressive deformation. Since the carcass is easily affected by compressive deformation, a common measure is to thicken the sidewall layer in the zone ZF and move the carcass away from the tire surface to suppress the effect of compressive deformation on the carcass. However, this measure not only makes it difficult to reduce the tire's weight, but also raises concerns that durability may decrease due to the promotion of heat storage. For this reason, in conventional tires, the thickness of the sidewall layer in the zone ZF is set in the range of 6 to 12 mm. In contrast, in the tire of the present invention, the average thickness F of the sidewall layer in the zone ZF satisfies the above-mentioned formula (1), so that the width BW of the belt and the thickness of the sidewall layer in the zone ZF are well balanced. The average thickness F of the sidewall layer is set to match the width BW of the belt. In other words, this tire can optimize the average thickness F while reducing the compression strain generated in the carcass. Since the average thickness F is set to a required thickness, the tire can be made lighter. Since the compression strain generated in the carcass is reduced, this tire can clear the requirements of the HLC standard. In particular, by setting the ratio (BW / SW) of the width BW of the belt to the cross-sectional width SW of the tire to be equal to the constant B expressed by formula (2), the tire 2 can clear the requirements of the HLC standard even if the average thickness F of the sidewall layer 6 in the zone ZF is set to 4 to 6 mm. This tire is made of a single carcass ply and uses a carcass with the radial height of the folded-up portion set to 17% or less of the tire's cross-sectional height. Despite this, the tire has the rigidity required to meet the requirements of the HLC standard while effectively thinning the sidewall layer in the bead portion. This tire can achieve improved durability without increasing the mass.

[0020] Preferably, the radial height of the pair of turn-up portions is 10 mm or more and 20 mm or less. This allows the carcass ply to be firmly fixed by the bead. The carcass can fully exert its function, which contributes to ensuring the rigidity required for the tire to clear the requirements of the HLC standard. The ends of the turn-up portions are positioned away from the vicinity of the zone ZF where large compressive strain occurs, which suppresses the occurrence of damage originating from the ends of the turn-up portions. This tire can have good durability.

[0021] Preferably, in the reference state, the angle that the folded portion makes with respect to the radial direction is equal to or greater than 15 degrees. This effectively prevents deformation of the folded-up portion due to the action of load, and prevents damage originating from the end of the folded-up portion, thereby providing the tire with good durability.

[0022] Preferably, the belt includes a number of parallel belt cords, and in the reference state, an angle of each of the belt cords with respect to the equator plane is 20 degrees or more and 32 degrees or less. This allows the belt to effectively contribute to suppressing the contour of the carcass from becoming distorted.

[0023] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0024] 1 shows a portion of a tire 2 according to one embodiment of the present invention. The tire 2 is a pneumatic tire for passenger cars. The tire 2 is a HIGH LOAD CAPACITY type tire defined in the ETRTO 2021 standard manual.

[0025] FIG. 1 shows a portion of a cross section of a tire 2 taken along a plane including the rotation axis (not shown) of the tire 2. The cross section shown in FIG. 1 is also called a meridian cross section. The direction indicated by the double arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double arrow RD is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, a dashed dotted line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0026] Fig. 1 shows a tire 2 mounted on a rim R. For example, air is filled between the tire 2 and the rim R, and the internal pressure of the tire 2 is adjusted. The rim R is a regular rim. The state of the tire 2 shown in Fig. 1 is the reference state described above.

[0027] In Fig. 1, the solid line BBL extending in the axial direction is the bead base line. This bead base line is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0028] 1, the position indicated by the symbol PC is an intersection point between an outer surface 2G of the tire 2 (specifically, a tread surface described later) and the equatorial plane. 1, when a groove is located on the equatorial plane, the equator PC is determined based on a virtual outer surface obtained assuming that there is no groove. The equator PC is the radially outer end of the tire 2. The equator PC of the tire 2 is determined with the tire 2 in a reference state. 1, the length indicated by the double arrow SH is the section height of the tire 2. The section height SH is represented as the radial distance from the bead base line to the equator PC of the tire 2. The section height SH of the tire 2 is expressed as the product of the nominal section width and the nominal aspect ratio.

[0029] In the present invention, the "nominal section width" and the "nominal aspect ratio" refer to the "nominal section width" and the "nominal aspect ratio" included in the "tire designation" defined in JIS D4202 "Automobile tires - Designation and specifications". For example, when the tire size of tire 2 is 205 / 55R16, the nominal section width of tire 2 is 205mm and the nominal aspect ratio is 55%. In this case, the section height SH of tire 2 is 112.75mm.

[0030] 1, the position indicated by the symbol PW is the axial outer end (hereinafter, the outer end PW) of the tire 2. When the outer surface has decoration such as a pattern or letters, the outer end PW is identified based on a virtual outer surface obtained by assuming that there is no decoration. The length indicated by the double-headed arrow SW in Fig. 1 is the section width of the tire 2. The section width SW is expressed as the axial distance from the first outer end PW to the second outer end PW. The section width SW is also the maximum width of the tire 2. The outer end PW is the position indicating the maximum width SW, and is also called the maximum width position PW. This section width SW of the tire 2 is specified for the tire 2 in a reference state.

[0031] The tire 2 includes a tread 4, a pair of sidewall layers 6, a pair of beads 8, a carcass 10, a belt 12, a band 14, a pair of chafers 16, and an inner liner 18.

[0032] The tread 4 is located radially outward of the carcass 10. The tread 4 is made of crosslinked rubber. The tread 4 comes into contact with the road surface at a tread surface 20. The tread 4 has a tread surface 20. An outer surface 2G of the tire 2 includes the tread surface 20. Grooves 22 are cut into the tread 4. This forms a tread pattern.

[0033] The tread 4 has a tread body 24 and a pair of wings 26 . Each wing 26 is located between the tread body 24 and the sidewall layer 6. The tread body 24 and the sidewall layer 6 are joined via the wing 26. The wing 26 is made of a crosslinked rubber in consideration of adhesiveness. The tread body 24 includes a cap portion 28 and a base portion 30 . The cap portion 28 includes the tread surface 20. The cap portion 28 comes into contact with the road surface. The cap portion 28 is made of crosslinked rubber that takes into consideration wear resistance and grip performance. The base portion 30 is located radially inside the cap portion 28. The base portion 30 is covered with the cap portion 28. The base portion 30 is made of a crosslinked rubber that has low heat buildup.

[0034] Each sidewall layer 6 is continuous with the tread 4. The sidewall layer 6 is located radially inward of the tread 4. The sidewall layer 6 is located axially outward of the carcass 10. The sidewall layer 6 has a sidewall body 32 and a clinch 34. A sidewall main body 32 is continuous with the tread 4. The sidewall main body 32 is made of crosslinked rubber in consideration of cut resistance. The clinch 34 is located radially inside the sidewall body 32. The clinch 34 contacts the rim R. The clinch 34 is made of crosslinked rubber in consideration of wear resistance.

[0035] Each bead 8 is located radially inward of the sidewall layer 6. Specifically, the bead 8 is located radially inward of the sidewall body 32 and axially inward of the clinch 34. The bead 8 includes a core 36 and an apex 38. The core 36 extends in the circumferential direction. Although not shown, the core 36 includes a steel wire. The apex 38 is located radially outward of the core 36. The apex 38 is made of crosslinked rubber having high rigidity. When one bead 8 of a pair of beads 8 is a first bead 8, the other bead 8 is a second bead 8.

[0036] The carcass 10 is located on the inside of the tread 4 and the pair of sidewall layers 6. The carcass 10 bridges between the pair of beads 8. The carcass 10 bridges between the first bead 8 and the second bead 8.

[0037] The carcass 10 is composed of one carcass ply 40. The carcass 10 of the tire 2 is lighter than a carcass including two or more carcass plies 40. The carcass ply 40 is turned up from the inside to the outside in the axial direction at each bead 8. The carcass ply 40 includes a ply body 42 that spans between the pair of cores 36, and a pair of turn-up portions 44 that are continuous with the ply body 42 and turned up at each of the cores 36.

[0038] 1, the length indicated by the double-headed arrow CH is the radial height of the turn-up portion 44. The radial height CH of the turn-up portion 44 is represented by the radial distance from the bead base line to the end of the turn-up portion 44. An end of the turn-up portion 44 of this tire 2 is located radially inward of the maximum width position PW. Specifically, the radial height CH of the turn-up portion 44 is 17% or less of the cross-sectional height SH of the tire 2. The carcass 10 of this tire 2 has a low turn-up structure (LTU structure). As described above, the carcass 10 is composed of one carcass ply 40. This carcass 10 can contribute to reducing the weight of the tire 2. From this viewpoint, the radial height CH of the turn-up portion 44 is preferably 15% or less of the cross-sectional height SH of the tire 2.

[0039] Although not shown, the carcass ply 40 includes a number of carcass cords arranged in parallel. These carcass cords cross the equatorial plane. The carcass cords span between the first bead 8 and the second bead 8. The carcass 10 of the tire 2 has a radial structure. Cords made of organic fibers are used as carcass cords in the tire 2. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0040] The belt 12 is located on the radially inner side of the tread 4. The belt 12 is located on the radially outer side of the carcass 10. The belt 12 is laminated on the carcass 10. 1, the double-headed arrow BW indicates the width of the belt 12. The width BW of the belt 12 is represented by the axial distance from one end of the belt 12 to the other end. In the tire 2, the ratio BW / SW of the width BW of the belt 12 to the cross-sectional width SW of the tire 2 is equal to or greater than 0.65 and equal to or less than 1.00. The ratio BW / SW is preferably equal to or greater than 0.70 and equal to or less than 0.95.

[0041] The belt 12 includes a plurality of belt plies 46 arranged in the radial direction. The plurality of belt plies 46 includes an inner belt ply 48 located at the innermost side and an outer belt ply 50 located at the outermost side. The belt 12 of the tire 2 is composed of two belt plies 46. In detail, the belt 12 is composed of the inner belt ply 48 and the outer belt ply 50. The inner belt ply 48 is laminated to the carcass 10 on the radially inner side of the tread 4. The outer belt ply 50 is laminated to the inner belt ply 48.

[0042] 1, an end of the outer belt ply 50 is located axially inward of an end of the inner belt ply 48. The outer belt ply 50 is narrower than the inner belt ply 48. The length from the end of the outer belt ply 50 to the end of the inner belt ply 48 is 3 mm or more and 10 mm or less. The width BW of the belt 12 described above is represented by the width of the wider inner belt ply 48.

[0043] Fig. 2 shows the configuration of the belt 12. In Fig. 2, the direction indicated by the double-headed arrow AD is the axial direction of the tire 2. The direction indicated by the double-headed arrow CD is the circumferential direction of the tire 2. The front side of the page is the radially outer side, and the back side is the radially inner side.

[0044] Each of the plurality of belt plies 46 constituting the belt 12 includes a large number of parallel belt cords 52. The belt cords 52 are steel cords. For convenience of explanation, the belt cords 52 are represented by solid lines, but the belt cords 52 are covered with a topping rubber 54. Each belt cord 52 is inclined with respect to the equatorial plane. The inclination direction of the belt cord 52 included in the outer belt ply 50 (hereinafter, outer belt cord 52s) is opposite to the inclination direction of the belt cord 52 included in the inner belt ply 48 (hereinafter, inner belt cord 52u).

[0045] The band 14 is laminated on the belt 12 on the inside of the tread 4. The end of the band 14 is located axially outward of the end of the belt 12. The length from the end of the belt 12 to the end of the band 14 is 3 mm or more and 7 mm or less.

[0046] The band 14 of the tire 2 includes a full band 56 and a pair of edge bands 58 . The full band 56 covers the entire belt 12 from the outside in the radial direction. The pair of edge bands 58 are disposed axially apart from each other across the equatorial plane. Each edge band 58 covers an end of the full band 56 from the outside in the radial direction. The band 14 may be composed of only the full band 56 or may be composed of only a pair of edge bands 58.

[0047] Although not shown, the band 14 includes a band cord wound in a spiral shape. In the band 14, the band cord extends substantially in the circumferential direction. Specifically, the angle that the band cord makes with the circumferential direction is 5° or less. The band 14 has a jointless structure. A cord made of an organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber. The band cord included in the full band 56 is the same as the band cord included in the edge band 58. The band cord of the full band 56 and the band cord of the edge band 58 may be different.

[0048] Each chafer 16 is located radially inward of the bead 8. The chafer 16 contacts the rim R. In the tire 2, the chafer 16 is made of a cloth and rubber impregnated into the cloth. 1, the inner end of the chafer 16 constitutes a part of the inner surface 2N of the tire. The outer end of the chafer 16 is located radially outward of the inner end. The outer end of the chafer 16 is located between the bead 8 and the clinch 34.

[0049] The inner liner 18 is positioned inside the carcass 10. The inner liner 18 constitutes the inner surface 2N of the tire 2. The inner liner 18 is made of crosslinked rubber having excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0050] Fig. 3 shows a part of the tire 2 shown in Fig. 1. Fig. 3 shows a bead portion of the tire 2. The position indicated by the symbol FN is a position on the outer surface 2G of the tire 2. The radial distance HN from the bead base line to the position FN is 20 mm. The position indicated by the symbol FG is a position on the outer surface 2G of the tire 2. The radial distance HG from the bead base line to the position FG is 30 mm. In Fig. 3, the zone from position FN to position FG is represented as zone ZF, which is a zone located at a radial distance from the bead base line of 20 mm to 30 mm. Position FN is the inner edge of zone ZF, and position FG is the outer edge of zone ZF. The position indicated by the symbol FC is the intersection point between the radial centerline of the zone ZF and the outer surface 2G of the tire 2. The position FC is the center of the zone ZF.

[0051] The action of the load causes strain in the tire 2. In particular, large compressive strain occurs near the zone ZF. To prevent damage to the bead portion, the sidewall layer 6 is configured to be thicker near the zone ZF than other portions.

[0052] 3, the length indicated by the double arrow TN is the thickness of the sidewall layer 6 at the inner end FN of the zone ZF. The length indicated by the double arrow TG is the thickness of the sidewall layer 6 at the outer end FG of the zone ZF. The length indicated by the double arrow TC is the thickness of the sidewall layer 6 at the center FC of the zone ZF. The thicknesses TN, TG, and TC are measured along a normal to the outer surface of the tire 2. In the present invention, the average thickness F of the sidewall layer 6 in the zone ZF is represented by the average value of the thickness TN, the thickness TG and the thickness TC.

[0053] The inventor noticed that the width BW of the belt affects the contour of the carcass (more specifically, the ply body), and that if the contour of the carcass becomes distorted, the distortion in the bead portion increases and the durability of the tire decreases. While adjusting the width BW of the belt, the inventor carefully considered what average thickness F the sidewall layer in the aforementioned zone ZF must have to ensure that the tire meets the requirements of the HIGH LOAD CAPACITY type (hereinafter, HLC standard) specified in the ETRTO 2021 standard manual. As a result, the inventor obtained the following relationship for the average thickness F of the sidewall layer 6 in the zone ZF.

[0054] That is, the average thickness F of the sidewall layer 6 in the zone ZF satisfies the following formula (1) expressed using a constant B, and the cross-sectional width SW of the tire 2 and the width BW of the belt 12 obtained in the standard state of the tire 2. Formula (1): 416×(BW / SW-B) 2 +4≦F≦416×(BW / SW-B) 2 +6 The average thickness F, the cross-sectional width SW, and the width BW are all in mm (millimeters).

[0055] Furthermore, the constant B satisfies the following formula (2) expressed using the aspect ratio RA of the tire 2. Formula (2): B=0.84×(-0.49×RA / 100+1.22) In addition, the aspect ratio RA in formula (2) is the "nominal aspect ratio." For example, if the tire size is 205 / 55R16, the nominal aspect ratio RA of this tire is 55%. In this case, the constant B is 0.80.

[0056] Average thickness F is 416 × (BW / SW-B) 2 If it is less than +4, there is a concern that the sidewall layer 6 in zone ZF will be too thin and the tire will not be able to meet the requirements of the HLC standard. Average thickness F is 416 × (BW / SW-B) 2 If it is greater than +6, there is a concern that the sidewall layer 6 in the zone ZF will become too thick, and the significance of adopting the carcass 10 having the LTU structure and consisting of one carcass ply 40 for the purpose of reducing weight will be lost. However, when the average thickness F satisfies the above-mentioned formula (1), the width BW of the belt 12 and the thickness of the sidewall layer 6 in the zone ZF are well balanced. The average thickness F of the sidewall layer 6 is set to match the width BW of the belt 12. In other words, the tire 2 can optimize the average thickness F while reducing the compression strain generated in the carcass 10. Since the average thickness F is set to a required thickness, the tire 2 can be made lighter. Since the compression strain generated in the carcass 10 is reduced, the tire 2 can meet the requirements of the HLC standard. In particular, by setting the ratio (BW / SW) of the width BW of the belt to the cross-sectional width SW of the tire 2 to be equal to the constant B expressed by formula (2), the tire 2 can meet the requirements of the HLC standard even if the average thickness F of the sidewall layer 6 in the zone ZF is set to 4 to 6 mm.

[0057] This tire 2 is made of a single carcass ply 40, and although it employs a carcass 10 having a low turn-up structure, it is possible to effectively thin the sidewall layer 6 in the bead portion while imparting to the tire 2 the rigidity required to clear the requirements of the HLC standard. The tire 2 can achieve improved durability without increasing the mass.

[0058] The radial height CH of the folded portion 44 is preferably 10 mm or more and 20 mm or less. By setting the radial height CH to 10 mm or more, the carcass ply 40 is firmly fixed by the beads 8. The carcass 10 can fully perform its function. The carcass 10 can contribute to ensuring the rigidity required for the tire 2 to clear the requirements of the HLC standard. By setting the radial height CH to 20 mm or less, the end of the turn-up portion 44 is disposed away from the vicinity of the zone ZF where large compressive strain occurs. This suppresses the occurrence of damage originating from the end of the turn-up portion 44. This tire 2 has good durability. From this viewpoint, it is more preferable that the radial height CH is 15 mm or less.

[0059] Fig. 4 shows a part of the tire 2 shown in Fig. 1. Fig. 4 shows a bead portion of the tire 2. 4, the position indicated by the symbol PF is the end of the folded portion 44. The position indicated by the symbol PB is the radially outer end of the contact surface between the folded portion 44 and the core 36. This radially outer end PB is the separation point where the folded portion 44 separates from the core 36 (hereinafter, the separation point of the folded portion 44). The solid line BFL is a straight line that passes through the separation point PB and the end PF of the folded portion 44. The solid line RFL is a straight line that passes through the end PF of the folded portion 44 and extends in the radial direction. The angle θf is the angle between the straight lines BFL and RFL. In the present invention, this angle θf is the angle that the folded portion 44 makes with respect to the radial direction.

[0060] In the reference state, the angle θf that the folded-back portion 44 forms with respect to the radial direction is preferably equal to or greater than 15 degrees. This effectively suppresses deformation of the folded-back portion 44 due to the action of load. Damage originating from the end of the folded-back portion 44 is suppressed. This tire 2 has good durability. From this viewpoint, the angle θf is more preferably equal to or greater than 17 degrees. From the viewpoint of suppressing damage originating from the end of the folded-back portion 44, it is preferable that the angle θf is larger. However, it is difficult to manufacture the tire 2 so that the angle θf exceeds 25 degrees in the reference state. From the viewpoint of being able to manufacture the tire 2, it is preferable that the angle θf is 25 degrees or less in the reference state.

[0061] From the viewpoint of effectively improving the durability of the tire 2 without increasing the mass, it is more preferable that the radial height CH of the folded-back portion 44 be 10 mm or more and 20 mm or less, and that the angle θf that the folded-back portion 44 makes with the radial direction in the standard state be 15 degrees or more.

[0062] As described above, the belt cord 52 is inclined with respect to the equatorial plane. In Fig. 2, angle θb represents the angle that the belt cord 52 included in the belt 12 makes with respect to the equatorial plane.

[0063] From the viewpoint that the belt 12 can effectively contribute to suppressing the contour of the carcass from becoming distorted, in the standard state, the angle θb of the belt cord 52 with respect to the equatorial plane is preferably 20 degrees or more and 32 degrees or less, and more preferably 24 degrees or more and 30 degrees or less. In this case, it is more preferable that the angle θb of the belt cord 52 included in the inner belt ply 48 with respect to the equatorial plane is the same as the angle θb of the belt cord 52 included in the outer belt ply 50 with respect to the equatorial plane.

[0064] As is clear from the above description, according to the present invention, a tire can be obtained that can improve durability without increasing mass. In particular, according to the present invention, a HIGH LOAD CAPACITY type tire defined in the ETRTO 2021 standard manual can be obtained that can improve durability without increasing mass. [Industrial Applicability]

[0065] The above-described technology capable of improving durability without increasing mass can be applied to various types of tires.

[0066] [Note] The present invention includes the following aspects.

[0067] [1] HIGH LOAD CAPACITY type tires as defined in the ETRTO 2021 standard manual, A pair of beads; a carcass extending between the pair of beads; A pair of sidewall layers located axially outboard of the carcass; A belt located radially outside the carcass; Equipped with Each of the pair of beads includes a core and an apex located radially outward of the core, The carcass is composed of one carcass ply, The carcass ply includes a ply body that spans between the pair of cores, and a pair of turn-up portions that are connected to the ply body and turned up around each of the cores, A radial height of the pair of folded-back portions is 17% or less of a cross-sectional height of the tire, The average thickness F of the sidewall layer in a zone from 20 mm to 30 mm in the radial direction from the bead base line satisfies the following formula (1), which is expressed using a constant B, and the tire section width SW and belt width BW obtained in a reference state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire. The constant B satisfies the following formula (2) expressed using the aspect ratio RA of the tire. tire. Formula (1): 416×(BW / SW-B) 2 +4≦F≦416×(BW / SW-B) 2 +6 Formula (2): B=0.84×(-0.49×RA / 100+1.22) [2] The tire described in [1] above, wherein the radial height of the pair of folded-up portions is 10 mm or more and 20 mm or less. [3] The tire according to [1] or [2] above, wherein in the reference state, the angle that the folded-back portion makes with respect to the radial direction is 15 degrees or more. [4] The belt includes a number of belt cords arranged in parallel, The tire according to any one of the above-mentioned [1] to [3], wherein in the reference state, an angle that each of the belt cords forms with respect to the equatorial plane is equal to or greater than 20 degrees and is equal to or less than 32 degrees. [Explanation of symbols]

[0068] 2. Tires 2G: Outer surface of tire 2N: Inner surface of tire 4. Tread 6. Sidewall layer 8...Bead 10. Carcass 12. Belt 14. Band 16. Chafer 18. Inner liner 20 Tread surface 32 Sidewall body 34. Clinch 36 cores 38. Apex 40···Carcass ply 42...Ply body 44... Folded part 46···Belt ply 48···Inner belt ply 50···Outer belt ply 52 Belt cord

Claims

1. A tire of HIGH LOAD CAPACITY type as defined in the ETRTO 2021 standard manual, A pair of beads; a carcass extending between the pair of beads; A pair of sidewall layers located axially outboard of the carcass; A belt located radially outside the carcass; Equipped with Each of the pair of beads includes a core and an apex located radially outward of the core, The carcass is composed of one carcass ply, The carcass ply includes a ply body that spans between a pair of the cores, and a pair of turn-up portions that are connected to the ply body and turned up at each of the cores, A radial height of the pair of folded-back portions is 17% or less of a cross-sectional height of the tire, The average thickness F of the sidewall layer in a zone from 20 mm to 30 mm in the radial direction from the bead base line satisfies the following formula (1), which is expressed using a constant B, and a section width SW of the tire and a belt width BW obtained in a reference state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire. The constant B satisfies the following formula (2) expressed using the aspect ratio RA of the tire. tire. Equation (1): 416 × (BW / SW - B) ２ + 4 ≤ F ≤ 416 × (BW / SW - B) ２ + 6 Formula (2): B=0.84×(-0.49×RA / 100+1.22)

2. The radial height of the pair of folded portions is 10 mm or more and 20 mm or less.

2. The tire of claim 1.

3. In the reference state, the angle that the folded portion forms with respect to the radial direction is 15 degrees or more.

2. The tire of claim 1.

4. The belt includes a number of belt cords arranged in parallel, In the reference state, an angle that each of the belt cords forms with respect to the equator plane is equal to or greater than 20 degrees and is equal to or less than 32 degrees. A tire according to any one of claims 1 to 3.

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