Tire

Abstract

The invention provides a tire. The tire (2) can realize durability improvement without increasing the mass. A tire (2) has a pair of beads (8), a carcass (10), a pair of sidewall layers (6), and a belt (12). A carcass ply (40) constituting a carcass (10) has a ply body (42) and a pair of folded portions (44). The radial height of the folded-back section (44) is 17% or less of the cross-sectional height of the tire (2). The average thickness (F) of the sidewall layer (6) in the region (ZF) satisfies formula (1) represented by a constant (B), the cross-sectional width (SW) of the tire (2), and the width (BW) of the belt (12). The constant (B) satisfies the following formula (2), and the formula (2) is represented by the flatness ratio (RA) of the tire (2). 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).

Description

Technical Field

[0001] The present invention relates to a tire. More specifically, the present invention relates to a tire mounted on a passenger vehicle. Background Art

[0002] The quality of the tire affects the rolling resistance. Considering the impact on the environment, tires with low rolling resistance are required.

[0003] When the number of carcass plies constituting the carcass is reduced or the length of the folded portion of the carcass ply is shortened in order to reduce the weight of the tire, the rigidity of the bead portion is reduced.

[0004] A large load acts on the bead portion of the tire. Moreover, the tire is repeatedly deformed and restored during driving. There is a concern that the bead portion is easily damaged. It is required to improve the durability of the bead portion.

[0005] If new elements are incorporated into the bead portion in order to improve the durability of the bead portion, the mass of the tire will increase.

[0006] Therefore, various studies have been conducted to establish a technology capable of maintaining the durability of the bead portion while achieving a reduction in tire weight (for example, see Patent Document 1 listed below).

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 9-286211 Summary of the invention

[0008] An object of the present invention is to provide a tire capable of achieving improved durability without increasing mass.

[0009] A tire of one embodiment of the present invention is a HIGH LOADCAPACITY type tire specified by the ETRTO standard manual 2021 (European Tire and Rim Technical Organization Standard Manual 2021 cf., https: / / www.etrto.org / Publications / Order). The tire comprises: a pair of beads; a carcass, which is erected between the pair of beads; a pair of sidewall layers, the pair of sidewall layers being located axially outside the carcass; and a belt, which is located radially outside the carcass. The pair of beads respectively have a core and an apex rubber located radially outside the core. The carcass is composed of one carcass ply. The carcass ply comprises: a ply main body, which is erected between a pair of cores; and a pair of folded parts, the pair of folded parts being connected to the ply main body and folded at each of the cores. The radial height of a pair of the folded parts is less than 17% of the cross-sectional height of the tire. The average thickness F of the sidewall layer in the region where the radial distance from the tire bead baseline is 20 mm to 30 mm satisfies the following formula (1), which is expressed using a constant B and a cross-sectional width SW of the tire and a width BW of the belt obtained under a reference state in which the tire is assembled on a regular rim and 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), which is expressed using the aspect ratio RA of the tire,

[0010] Formula (1): 416 × (BW / SW-B) 2 +4≤F≤416× (BW / SW-B) 2 +6

[0011] Formula (2): B = 0.84 × (-0.49 × RA / 100 + 1.22).

[0012] According to the present invention, it is possible to obtain a tire capable of achieving improved durability without increasing mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a cross-sectional view showing a portion of a tire according to an embodiment of the present invention.

[0014] Figure 2 This is a schematic diagram illustrating the structure of the belt.

[0015] Figure 3 It is an enlarged cross-sectional view showing a bead portion.

[0016] Figure 4 It is an enlarged cross-sectional view showing a bead portion.

[0017] Description of symbols

[0018] 2: tire; 2G: tire outer surface; 2N: tire inner surface; 4: tread; 6: sidewall layer; 8: bead; 10: carcass; 12: belt; 14: cap band; 16: bead cover; 18: inner liner; 20: tread surface; 32: sidewall body; 34: edge; 36: core; 38: apex; 40: carcass ply; 42: ply body; 44: turnback; 46: belt ply; 48: inner belt ply; 50: outer belt ply; 52: belt cord. DETAILED DESCRIPTION

[0019] The tire of the present invention is assembled to a rim. Air is filled inside the tire to adjust the internal pressure of the tire. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly has a rim and a tire assembled to the rim.

[0020] In the present invention, a state in which a tire is assembled on a regular rim, the internal pressure of the tire is adjusted to a regular internal pressure, and no load is applied to the tire is referred to as a regular state.

[0021] The state in which a tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire is referred to as a reference state.

[0022] In the present invention, unless otherwise specified, the dimensions and angles of various parts of the tire are measured under normal conditions.

[0023] The dimensions and angles of various parts in the meridian cross section of the tire that cannot be measured when the tire is assembled on a regular rim are measured in a cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set in a manner that the distance between the left and right beads is consistent with the distance between the beads of a tire assembled on a regular rim. In addition, the structure of the tire that cannot be confirmed when the tire is assembled on a regular rim is confirmed in the aforementioned cut surface.

[0024] A regular rim is a rim specified in the standards that the tire complies with. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are regular rims.

[0025] The normal internal pressure is the internal pressure specified in the standard that the tire complies with. The "maximum pressure" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIATION COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal internal pressures.

[0026] The normal load is the load specified in the standards that the tire complies with. The "maximum load capacity" in the JATMA standards, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIATION COLD INFLATION PRESSURES" in the TRA standards, and the "LOAD CAPACITY" in the ETRTO standards are normal loads.

[0027] In the present invention, unless otherwise specified, the load index (LI) is the load index used for HIGH LOAD CAPACITY type tires (hereinafter referred to as HLC type tires) specified by ETRTO standard manual 2021, and is an index that represents the maximum mass (i.e., maximum load capacity) allowed to be loaded on the tire under specified conditions.

[0028] In the present invention, the tread portion of the tire refers to the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that engages with the rim. The sidewall portion refers to the portion of the tire that is mounted between the tread portion and the bead portion. The tire has a tread portion, a pair of bead portions, and a pair of sidewall portions as portions.

[0029] [Foundation underlying the present invention]

[0030] Considering the impact on the environment, electric vehicles are becoming more popular. Electric vehicles are equipped with batteries. Batteries that can travel a distance of about 500 km are heavy. Therefore, electric vehicles tend to be heavier than conventional gasoline vehicles. Therefore, a higher load acts on tires installed on electric vehicles than on tires installed on gasoline vehicles.

[0031] In order to provide tires that can withstand high loads, the load index was re-evaluated in the ETRTO standard, and high load capacity type (hereinafter referred to as HLC type) tires were introduced as a new category.

[0032] In order to be accepted as an HLC type tire, the tire must be able to withstand higher loads than before.

[0033] To this end, the rigidity of the tire must be increased. However, if the rigidity of the tire is increased, there is a concern that the mass of the tire will increase as described above.

[0034] Therefore, the inventors confirmed the ratio of the belt width to the cross-sectional width of the tire and the thickness of the sidewall layer of the bead portion, and found that the two are related. As long as the belt width is within an appropriate range relative to the cross-sectional width of the tire, even if a carcass consisting of a single carcass cord layer and having a low turn-up (LTU) structure is used, the required rigidity can be imparted to the tire and the sidewall layer of the bead portion can be thinned, thereby completing the invention described below.

[0035] [Overview of Embodiments of the Invention]

[0036] The present invention is a HIGH LOAD CAPACITY type tire specified by ETRTO standard manual 2021, wherein the tire comprises: a pair of beads; a carcass, which is arranged between the pair of beads; a pair of sidewall layers, the pair of sidewall layers are located axially outside the carcass; and a belt, which is located radially outside the carcass, the pair of beads respectively have a core and an apex located radially outside the core, the carcass is composed of a carcass ply, and the carcass ply has: a ply main body, which is arranged between the pair of cores; and a pair of folded parts, the pair of folded parts are connected to the ply main body and folded at each of the cores, and the pair of folded parts are connected to the ply main body and folded at each of the cores. The radial height of the return portion is less than 17% of the cross-sectional height of the tire, the average thickness F of the sidewall layer in the region where the radial distance from the tire bead baseline is 20 mm to 30 mm satisfies the following formula (1), which is expressed using a constant B and a cross-sectional width SW and a belt width BW of the tire obtained under a reference state in which the tire is assembled on a regular rim and 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), which is expressed using the aspect ratio RA of the tire,

[0037] Formula (1): 416×(BW / SW-B) 2 +4≤F≤416×(BW / SW-B) 2 +6

[0038] Formula (2): B = 0.84 × (-0.49 × RA / 100 + 1.22).

[0039] The tire of the present invention can achieve improved durability without increasing mass. The mechanism by which such an effect is achieved is not yet clear, but is presumed as follows.

[0040] In a rolling tire, compression deformation is repeatedly performed on the surface portion of the area ZF. Since the carcass is easily affected by compression deformation, the following countermeasure is generally implemented: by making the sidewall layer in the area ZF thicker, the carcass is moved away from the surface of the tire, thereby suppressing the influence of compression deformation on the carcass. However, this countermeasure is not only difficult to achieve lightweight tires, but also promotes heat storage, so there is a concern that durability will be reduced. Therefore, in existing tires, the thickness of the sidewall layer in the area ZF is set in the range of 6mm to 12mm.

[0041] In contrast, in the tire of the present invention, by making the average thickness F of the sidewall layer in the area ZF satisfy the above-mentioned formula (1), the width BW of the belt and the thickness of the sidewall layer in the area ZF can be balanced. The average thickness F of the sidewall layer is set corresponding to the width BW of the belt. In other words, the tire can reduce the compression deformation generated in the carcass and optimize the average thickness F. Since the average thickness F is set to the required thickness, the tire can be lightweight. Since the compression deformation generated in the carcass is reduced, the tire can meet the requirements of the HLC standard. In particular, by setting the ratio of the width BW of the belt to the cross-sectional width SW of the tire (BW / SW) to be equal to the constant B represented by formula (2), even if the average thickness F of the sidewall layer in the area ZF is set to 4mm to 6mm, the tire can meet the requirements of the HLC standard.

[0042] Although this tire uses a carcass composed of one carcass ply and the radial height of the folded portion is set to be less than 17% of the tire's cross-sectional height, it has the rigidity required to meet the requirements of the HLC standard and can effectively make the sidewall layer of the bead portion thinner.

[0043] The tire can achieve improved durability without an accompanying increase in mass.

[0044] Preferably, the radial height of a pair of the folded portions is not less than 10 mm and not more than 20 mm. Thus, the carcass cord layer is firmly fixed by the tire bead. The carcass can fully exert its function, thereby helping to ensure the rigidity required for the tire to meet the requirements of the HLC standard. Since the end of the folded portion is arranged away from the vicinity of the area ZF where large compression deformation occurs, the occurrence of damage starting from the end of the folded portion is suppressed. The tire can have good durability.

[0045] Preferably, in the reference state, an angle formed by the folded portion with respect to a radial direction is greater than or equal to 15 degrees.

[0046] This effectively suppresses deformation of the folded portion due to the action of the load. Since damage starting from the end of the folded portion is suppressed, the tire can have good durability.

[0047] Preferably, the belt includes a plurality of parallel belt cords, and in the reference state, the angle formed by each of the belt cords with respect to the equatorial plane is 20 degrees or more and 32 degrees or less. Thus, the belt can effectively contribute to suppressing deformation of the carcass profile.

[0048] [Details of the embodiments of the present invention]

[0049] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0050] Figure 1 A portion of a tire 2 according to an embodiment of the present invention is shown. The tire 2 is a pneumatic tire for a passenger car. The tire 2 is a HIGH LOAD CAPACITY type tire specified in ETRTO standard manual 2021.

[0051] Figure 1 A portion of a cross section of a tire 2 along a plane containing the axis of rotation (not shown) of the tire 2 is shown. Figure 1 The cross section shown 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 refers to the 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. Figure 1 The direction perpendicular to the paper surface is the circumferential direction of the tire 2 .

[0052] exist Figure 1 In FIG. 2 , a dashed line CL extending in the radial direction indicates the equatorial plane CL of the tire 2 .

[0053] Figure 1 The tire 2 is shown assembled to the rim R. For example, air is filled between the tire 2 and the rim R to adjust the internal pressure of the tire 2. The rim R is a regular rim. Figure 1 The state of the tire 2 shown is the above-mentioned reference state.

[0054] exist Figure 1 In FIG. 1 , a solid line BBL extending in the axial direction is a bead base line BBL. The bead base line BBL is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0055] exist Figure 1 In FIG. 1 , the position indicated by reference numeral PC is the intersection of the outer surface 2G of the tire 2 (specifically, the tread surface described later) and the equatorial plane CL. The intersection PC is the equator of the tire 2 .

[0056] like Figure 1As shown, when the grooves are located on the equatorial plane CL, the equator PC is determined based on an imaginary outer surface assumed to have no grooves. The equator PC is the radial outer end of the tire 2. The equator PC of the tire 2 is determined in the tire 2 in the reference state.

[0057] Figure 1 The length indicated by the double arrow SH is the section height of the tire 2. The section height SH is represented by the radial distance from the bead base line BBL to the equator PC of the tire 2.

[0058] The cross-sectional height SH of the tire 2 is represented by the product of the nominal cross-sectional width and the nominal aspect ratio.

[0059] In the present invention, "nominal section width" and "nominal aspect ratio" refer to "nominal section width" and "nominal aspect ratio" included in "nominal tires" specified in JISD4202 "Automobile tires - nominal method and specifications". For example, when the tire size of the tire 2 is 205 / 55R16, the nominal section width of the tire 2 is 205 mm, and the nominal aspect ratio is 55%. In this case, the section height SH of the tire 2 is 112.75 mm.

[0060] Figure 1 The position indicated by the middle symbol PW is the axial outer end (hereinafter referred to as outer end PW) of the tire 2. When the outer surface 2G has decorations such as patterns and letters, the outer end PW is determined based on a virtual outer surface assuming that there is no decoration.

[0061] Figure 1 The length indicated by the double arrow SW is the cross-sectional width of the tire 2. The cross-sectional width SW is represented by the axial distance from the first outer end PW to the second outer end PW. The cross-sectional width SW is also the maximum width of the tire 2. The outer end PW is the position indicating the maximum width SW, also referred to as the maximum width position PW. The cross-sectional width SW of the tire 2 is determined in the tire 2 in the reference state.

[0062] 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 cap band 14 , a pair of chafers 16 , and an inner liner 18 .

[0063] The tread 4 is located radially outside the carcass 10. The tread 4 is made of a cross-linked rubber. The tread 4 contacts the road surface at a tread surface 20. The tread 4 has the tread surface 20. The outer surface 2G of the tire 2 includes the tread surface 20.

[0064] Grooves 22 are engraved on the tread 4. Thus, a tread pattern is formed.

[0065] The tread 4 includes a tread body 24 and a pair of wing portions 26 .

[0066] Each wing portion 26 is located between the tread body 24 and the sidewall layer 6. The tread body 24 and the sidewall layer 6 are bonded via the wing portion 26. The wing portion 26 is made of a cross-linked rubber in consideration of adhesiveness.

[0067] The tread body 24 has a top portion 28 and a base portion 30 .

[0068] The top portion 28 includes the tread surface 20. The top portion 28 contacts the road surface. The top portion 28 is made of cross-linked rubber in consideration of wear resistance and grip performance.

[0069] The base portion 30 is located radially inward of the top portion 28. The base portion 30 is covered by the top portion 28. The base portion 30 is made of a cross-linked rubber having low heat build-up properties.

[0070] Each sidewall layer 6 is connected to 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 bead portion 34.

[0071] The sidewall body 32 is connected to the tread 4. The sidewall body 32 is made of a cross-linked rubber in consideration of cut resistance.

[0072] The bead portion 34 is located radially inward of the sidewall main body 32. The bead portion 34 is in contact with the rim R. The bead portion 34 is made of a cross-linked rubber in consideration of wear resistance.

[0073] 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 bead portion 34.

[0074] The tire bead 8 has 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 outside the core 36. The apex 38 is made of a cross-linked rubber having high rigidity. When one of the tire bead 8 of the pair of tire bead 8 is the first tire bead 8, the other tire bead 8 is the second tire bead 8.

[0075] The carcass 10 is located inside the tread 4 and the pair of sidewall layers 6. The carcass 10 is laid between the pair of beads 8. The carcass 10 is laid between the first bead 8 and the second bead 8.

[0076] The carcass 10 is composed of a single carcass ply 40. The carcass 10 of the tire 2 is lighter than a carcass including two or more carcass plies 40.

[0077] The carcass ply 40 is folded back from the axial inner side to the outer side at each bead 8. The carcass ply 40 includes a ply main body 42 spanning between the pair of cores 36 and a pair of folded back portions 44 connected to the ply main body 42 and folded back at each core 36.

[0078] Figure 1The length indicated by the double arrow CH is the radial height of the turn-back portion 44. The radial height CH of the turn-back portion 44 is represented by the radial distance from the bead base line BBL to the end of the turn-back portion 44.

[0079] The end of the folded portion 44 of the tire 2 is located radially inside the maximum width position PW. Specifically, the radial height CH of the folded portion 44 is less than 17% of the cross-sectional height SH of the tire 2. The carcass 10 of the tire 2 has a low turn-up structure (LTU structure). As described above, the carcass 10 is composed of one carcass cord layer 40. The carcass 10 can contribute to the weight reduction of the tire 2. From this point of view, the radial height CH of the folded portion 44 is preferably less than 15% of the cross-sectional height SH of the tire 2.

[0080] Although not shown, the carcass ply 40 includes a plurality of carcass cords arranged in parallel. These carcass cords intersect the equatorial plane CL. The carcass cords are laid between the first bead 8 and the second bead 8. The carcass 10 of the tire 2 has a radial structure.

[0081] 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.

[0082] The belt 12 is located radially inside the tread 4. The belt 12 is located radially outside the carcass 10. The belt 12 is laminated on the carcass 10.

[0083] Figure 1 The double arrow BW in the middle is 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.

[0084] In the tire 2, a ratio BW / SW of the width BW of the belt 12 to the cross-sectional width SW of the tire 2 is 0.65 or more and 1.00 or less. The ratio BW / SW is preferably 0.70 or more and 0.95 or less.

[0085] The belt 12 has a plurality of belt plies 46 arranged in the radial direction. The plurality of belt plies 46 include 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. Specifically, the belt 12 is composed of the inner belt ply 48 and the outer belt ply 50.

[0086] The inner belt ply 48 is laminated on the carcass 10 on the radially inner side of the tread 4. The outer belt ply 50 is laminated on the inner belt ply 48.

[0087] like Figure 1As shown, the end of the outer belt ply 50 is located axially inward of the 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 is represented by the width of the wide inner belt ply 48.

[0088] Figure 2 The structure of the belt 12 is shown. Figure 2 The direction indicated by the double arrow AD is the axial direction of the tire 2. The direction indicated by the double arrow CD is the circumferential direction of the tire 2. The front side of the paper is the radially outer side, and the back side is the radially inner side.

[0089] The plurality of belt plies 46 constituting the belt 12 each include a plurality of parallel belt cords 52. The belt cords 52 are steel cords. For ease of explanation, the belt cords 52 are indicated by solid lines, but the belt cords 52 are covered with topping rubber 54.

[0090] Each belt cord 52 is inclined with respect to the equatorial plane CL. The inclination direction of the belt cords 52 included in the outer belt ply 50 (hereinafter referred to as outer belt cords 52s) and the inclination direction of the belt cords 52 included in the inner belt ply 48 (hereinafter referred to as inner belt cords 52u) are opposite to each other.

[0091] The cap band 14 is laminated on the belt 12 inside the tread 4. The end of the cap band 14 is located axially outside the end of the belt 12. The length from the end of the belt 12 to the end of the cap band 14 is 3 mm or more and 7 mm or less.

[0092] The cap band 14 of the tire 2 includes a full cap band 52 and a pair of edge cap bands 54 .

[0093] The full band 52 covers the entire belt 12 from the outside in the radial direction.

[0094] The pair of edge bands 54 are arranged to be separated in the axial direction across the equatorial plane CL. Each edge band 54 covers the end of the full band 52 from the outside in the radial direction.

[0095] The cap band 14 may be composed of only the full cap band 52 or only the pair of edge cap bands 54 .

[0096] Although not shown, the cap band 14 includes a cap band cord wound in a spiral shape. In the cap band 14, the cap band cord substantially extends in the circumferential direction. Specifically, the angle formed by the cap band cord relative to the circumferential direction is 5° or less. The cap band 14 has a seamless structure. A cord composed of organic fibers is used as the cap band cord. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0097] The band cords included in the full band 52 are the same as the band cords included in the edge band 54. The band cords of the full band 52 and the band cords of the edge band 54 may be different.

[0098] Each chafer 16 is located radially inward of the bead 8. The chafer 16 is in contact with the rim R. In the tire 2, the chafer 16 is composed of cloth and rubber impregnated in the cloth.

[0099] like Figure 1 As shown, the inner end of the chafer 16 constitutes a part of the inner surface 2N of the tire 2. The outer end of the chafer 16 is located radially outside the inner end thereof. The outer end of the chafer 16 is located between the bead 8 and the bead portion 34.

[0100] The inner liner 18 is located inside the carcass 10. The inner liner 18 constitutes the inner surface 2N of the tire 2. The inner liner 18 is made of a cross-linked rubber having excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0101] Figure 3 Shows Figure 1 A portion of a tire 2 is shown. Figure 3 A bead portion of the tire 2 is shown.

[0102] The position indicated by reference numeral FN is a position on the outer surface 2G of the tire 2. A radial distance HN from the bead base line BBL to the position FN is 20 mm.

[0103] The position indicated by reference numeral FG is a position on the outer surface 2G of the tire 2. A radial distance HG from the bead base line BBL to the position FG is 30 mm.

[0104] Figure 3 The area from the position FN to the position FG is indicated as a zone ZF. The zone ZF is an area having a radial distance of 20 mm to 30 mm from the bead base line BBL.

[0105] Position FN is the inner end of area ZF, and position FG is the outer end of area ZF.

[0106] The position indicated by reference numeral FC is the intersection of the radial center line of the zone ZF and the outer surface 2G of the tire 2. The position FC is the center of the zone ZF.

[0107] The tire 2 is deformed by the load. In particular, a large compressive deformation occurs near the region ZF. In order to prevent damage to the bead portion, the sidewall layer 6 is configured to be thicker near the region ZF than other portions.

[0108] Figure 3The 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 thickness TN, the thickness TG, and the thickness TC are measured along the normal to the outer surface of the tire 2.

[0109] In the present invention, the average thickness F of the sidewall layer 6 in the region ZF is represented by the average value of the thickness TN, the thickness TG, and the thickness TC.

[0110] The inventors of the present invention focused on the fact that the width BW of the belt will affect the profile of the carcass (specifically, the main body of the cord layer). If the profile of the carcass is deformed, the deformation in the bead portion will increase and the durability of the tire will decrease. Therefore, they conducted in-depth research on whether the tire can meet the requirements of LOAD CAPACITY HIGHtype (hereinafter referred to as the HLC standard) specified in the ETRTO standard manual 2021 if the sidewall layer in the above-mentioned area ZF has at least a certain degree of average thickness F while adjusting the width BW of the belt. As a result, the following relationship was obtained for the average thickness F of the sidewall layer 6 in the area ZF.

[0111] That is, the average thickness F of the sidewall layer 6 in the region 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 reference state of the tire 2 .

[0112] Formula (1): 416×(BW / SW-B) 2 +4≤F≤416×(BW / SW-B) 2 +6

[0113] In addition, the units of the average thickness F, the cross-sectional width SW, and the width BW are mm (millimeter).

[0114] Furthermore, the constant B satisfies the following formula (2), which is expressed using the aspect ratio RA of the tire 2 .

[0115] Formula (2): B = 0.84 × (-0.49 × RA / 100 + 1.22)

[0116] In addition, the aspect ratio RA in the formula (2) uses the "nominal aspect ratio". For example, when the tire size of the tire is 205 / 55R16, the nominal aspect ratio RA of the tire is 55%. In this case, the constant B is 0.80.

[0117] When the average thickness F is less than 416×(BW / SW-B) 2In the case of +4, the sidewall layer 6 in the region ZF becomes too thin, and the tire may fail to meet the requirements of the HLC standard.

[0118] When the average thickness F is greater than 416×(BW / SW-B) 2 In the case of +6, the sidewall layer 6 in the region ZF becomes too thick, and there is a possibility that the meaning of adopting the carcass 10 composed of one carcass ply 40 and having the LTU structure is lost for the purpose of weight reduction.

[0119] 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 area ZF can be adjusted in a balanced manner. The average thickness F of the sidewall layer 6 is set to correspond to the width BW of the belt 12. In other words, the tire 2 can reduce the compression deformation generated in the carcass 10 and optimize the average thickness F. Since the average thickness F is set to the required thickness, the tire 2 can be lightweight. Since the compression deformation 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 12 to the cross-sectional width SW of the tire 2 to be equal to the constant B represented by formula (2), even if the average thickness F of the sidewall layer 6 in the area ZF is set to 4mm to 6mm, the tire 2 can meet the requirements of the HLC standard.

[0120] Although the tire 2 uses the carcass 10 composed of one carcass ply 40 and having a turned-up structure, the tire 2 can be provided with the rigidity required to meet the requirements of the HLC standard and the sidewall layer 6 of the bead portion can be effectively thinned.

[0121] The tire 2 can achieve improved durability without increasing mass.

[0122] The radial height CH of the folded portion 44 is preferably not less than 10 mm and not more than 20 mm.

[0123] 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 exert its function. The carcass 10 can help ensure the rigidity required for the tire 2 to meet the requirements of the HLC standard.

[0124] By setting the radial height CH to be less than 20 mm, the end of the folded portion 44 is arranged away from the vicinity of the region ZF where large compression deformation occurs. The occurrence of damage starting from the end of the folded portion 44 is suppressed. The tire 2 has good durability. From this point of view, the radial height CH is more preferably less than 15 mm.

[0125] Figure 4 Shows Figure 1A portion of a tire 2 is shown. Figure 4 A bead portion of the tire 2 is shown.

[0126] Figure 4 The position indicated by the middle symbol PF is the end of the return portion 44. The position indicated by the symbol PB is the radial outer end of the contact surface between the return portion 44 and the core 36. The radial outer end PB is the separation point where the return portion 44 leaves the core 36 (hereinafter referred to as the separation point of the return portion 44). Moreover, the solid line BFL is a straight line passing through the separation point PB and the end PF of the return portion 44. The solid line RFL is a straight line passing through the end PF of the return portion 44 and extending radially.

[0127] The angle θf is the angle formed by the straight line BFL and the straight line RFL.

[0128] In the present invention, the angle θf is an angle formed by the folded portion 44 with respect to the radial direction.

[0129] In the reference state, the angle θf formed by the folding portion 44 relative to the radial direction is preferably greater than 15 degrees. Thus, deformation of the folding portion 44 caused by the action of the load is effectively suppressed. Damage starting from the end of the folding portion 44 is suppressed. The tire 2 has good durability. From this point of view, the angle θf is more preferably greater than 17 degrees.

[0130] From the viewpoint of being able to suppress damage starting from the end of the folded portion 44, the larger the angle θf, the better. However, it is difficult to manufacture the tire 2 in such a manner that the angle θf exceeds 25 degrees in the reference state. From the viewpoint of being able to manufacture the tire 2, the angle θf is preferably 25 degrees or less in the reference state.

[0131] From the viewpoint of effectively improving the durability of the tire 2 without increasing the mass, it is more preferred that the radial height CH of the folded portion 44 is greater than or equal to 10 mm and less than or equal to 20 mm, and in the reference state, the angle θf formed by the folded portion 44 with respect to the radial direction is greater than or equal to 15 degrees.

[0132] As described above, the belt cords 52 are inclined relative to the equatorial plane CL. Figure 2 In FIG. 8 , the angle θb represents the angle formed by the belt cords 52 included in the belt 12 with respect to the equatorial plane CL.

[0133] From the viewpoint that the belt 12 can effectively contribute to suppressing the contour deformation of the carcass 10, in the reference state, the angle θb formed by the belt cords 52 with respect to the equatorial plane CL 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 formed by the belt cords 52 included in the inner belt ply 48 with respect to the equatorial plane CL is the same as the angle θb formed by the belt cords 52 included in the outer belt ply 50 with respect to the equatorial plane CL.

[0134] As can be seen from the above description, according to the present invention, a tire capable of achieving improved durability without increasing mass can be obtained. In particular, according to the present invention, a HIGH LOAD CAPACITY type tire specified in the ETRTO standard manual 2021 capable of achieving improved durability without increasing mass can be obtained.

[0135] Industrial Applicability

[0136] The above-described technology capable of improving durability without increasing mass can be applied to various tires.

[0137] [Note]

[0138] The present invention includes the following aspects.

[0139] [1] A tire, which is a HIGH LOADCAPACITY type tire specified in the ETRTO standard manual 2021, wherein:

[0140] The tire features:

[0141] A pair of tire beads;

[0142] A carcass, which is mounted between the pair of beads;

[0143] a pair of sidewall layers, the pair of sidewall layers being located axially outward of the carcass; and

[0144] a belt located radially outside the carcass,

[0145] The pair of tire beads respectively have a core and an apex located radially outside the core,

[0146] The carcass is composed of a carcass ply.

[0147] The carcass ply has:

[0148] a carcass ply body mounted between the pair of cores; and

[0149] a pair of folded portions connected to the carcass main body and folded at each of the cores,

[0150] The radial height of the pair of folded portions is less than 17% of the cross-sectional height of the tire,

[0151] The average thickness F of the sidewall layer in the region where the radial distance from the bead base line is 20 mm to 30 mm satisfies the following formula (1), which is expressed using a constant B and a cross-sectional width SW of the tire and a width BW of the belt obtained under a reference state in which the tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 290 kPa, and no load is applied to the tire,

[0152] The constant B satisfies the following formula (2), which is expressed using the aspect ratio RA of the tire:

[0153] Formula (1): 416×(BW / SW-B) 2 +4≤F≤416×(BW / SW-B) 2 +6

[0154] Formula (2): B = 0.84 × (-0.49 × RA / 100 + 1.22).

[0155] [2] The tire according to [1], wherein:

[0156] A radial height of the pair of folded portions is greater than or equal to 10 mm and less than or equal to 20 mm.

[0157] [3] The tire according to [1] or [2], wherein:

[0158] In the reference state, an angle formed by the folded portion with respect to a radial direction is greater than or equal to 15 degrees.

[0159] [4] The tire according to any one of [1] to [3], wherein:

[0160] The belt comprises a plurality of belt cords arranged in parallel.

[0161] In the reference state, the angle formed by each of the belt cords with respect to the equatorial plane is not less than 20 degrees and not more than 32 degrees.

Claims

1. A tire, which is a HIGH LOAD CAPACITY type tire specified by ETRTO standard manual 2021, wherein: The tire features: A pair of tire beads; A carcass, which is mounted between the pair of beads; a pair of sidewall layers, the pair of sidewall layers being located axially outward of the carcass; and a belt located radially outside the carcass, The pair of tire beads respectively have a core and an apex located radially outside the core, The carcass is composed of a carcass ply. The carcass ply has: a carcass ply body mounted between the pair of cores; and a pair of folded portions connected to the carcass main body and folded at each of the cores, The radial height of the pair of folded portions is less than 17% of the cross-sectional height of the tire, The average thickness F of the sidewall layer in the region where the radial distance from the bead base line is 20 mm to 30 mm satisfies the following formula (1), which is expressed using a constant B and a cross-sectional width SW of the tire and a width BW of the belt obtained under a reference state in which the tire is assembled 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), which is expressed using the aspect ratio RA of the 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 tire according to claim 1, wherein: A radial height of the pair of folded portions is greater than or equal to 10 mm and less than or equal to 20 mm.

3. The tire according to claim 1, wherein: In the reference state, an angle formed by the folded portion with respect to a radial direction is greater than or equal to 15 degrees.

4. The tire according to any one of claims 1 to 3, wherein: The belt comprises a plurality of belt cords arranged in parallel. In the reference state, the angle formed by each of the belt cords with respect to the equatorial plane is not less than 20 degrees and not more than 32 degrees.

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