tire

Abstract

To provide a tire 2 capable of achieving improvement in turning performance.SOLUTION: An outer surface 2G of a tire 2 includes a tread surface 22 and a pair of side surfaces 26. A position, on the tread surface 22, at which an axial direction distance from an equatorial plane is 60% of an axial direction distance from the equatorial plane to a reference ground-contact position PH, is an inclination confirmation position P60. In a meridian cross section, an angle formed by a tangent to the contour line of the tread surface 22 at the inclination confirmation position P60 with respect to an axial direction is 2.5 degrees or greater and 3.5 degrees or less. In a ground-contact surface, the ratio of an equatorial ground-contact length measured along the equatorial plane to a reference ground-contact length at a position corresponding to a width of 60% of the ground-contact width of the ground-contact surface is a shape index F60. The shape index F60 is 1.00 or greater and 1.20 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a tire. More specifically, the present invention relates to a tire considering use in sports driving.

Background Art

[0002] In order to improve performance such as high-speed durability and handling stability, for example, the contour line of the tread surface (also referred to as the tread profile) is adjusted (for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In sports driving on a circuit or the like, it is required that the vehicle can turn at a higher speed. For this purpose, it has been considered to increase the cornering force generated during turning in a tire.

[0005] The inventor of the present invention confirmed the force generation situation on the grounding surface during turning using the finite element method (Finite Element Method (FEM)). As a result, it was found that a force in the opposite direction to the turning direction occurs in a part of the grounding surface. The force in the opposite direction to the turning direction reduces the cornering force. In other words, if the generation of the force in the opposite direction to the turning direction can be suppressed, the cornering force can be further increased. In this case, the tire can contribute to the improvement of the turning performance of the vehicle.

[0006] The present invention has been made in view of such circumstances. An object of the present invention is to provide a tire capable of achieving an improvement in turning performance. [[ID=​​

[0007] The tire according to the present invention comprises a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass. The outer surface of the tire comprises a tread surface that contacts the road surface and a pair of side surfaces connected to the tread surface. The reference contact position is obtained by mounting the tire on a regular rim, adjusting the internal pressure of the tire to 92% of the regular internal pressure, and applying a load of 70% of the regular load to the tire, thereby bringing the tire into contact with a plane, and positioning the tire on the tread surface corresponding to the contact edge of the tire's contact surface. The inclination confirmation position is the position on the tread surface where the axial distance from the equatorial plane is 60% of the axial distance from the equatorial plane to the reference contact position. In the meridional cross-section of the tire, the angle made with the tangent to the contour line of the tread surface at the inclination confirmation position is 2.5 degrees or more and 3.5 degrees or less. In the aforementioned grounding surface, the ratio of the equatorial grounding length measured along the equatorial plane to the reference grounding length at a position corresponding to 60% of the grounding width of the grounding surface is the shape index F60, and the shape index F60 is 1.00 or more and 1.20 or less. [Effects of the Invention]

[0008] According to the present invention, a tire can be obtained that can achieve improved turning performance. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing a part of a tire relating to one embodiment of the present invention. [Figure 2] This is a cross-sectional view illustrating the contour lines of the tread surface. [Figure 3] This is a schematic diagram showing the shape of the tire's contact patch. [Modes for carrying out the invention]

[0010] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0011] The tire of the present invention is mounted on a rim. The inside of the tire is filled with air, and the internal pressure of the tire is regulated. In this disclosure, the tire mounted on a rim is a tire-rim assembly. The tire-rim assembly comprises a rim and a tire mounted on the rim.

[0012] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state. A tire mounted on a standard rim, with its internal pressure adjusted to 92% of the standard internal pressure, and without any load applied to it, is considered to be in a standard condition. When a tire is mounted on a standard rim, its internal pressure is adjusted to 5% of the standard internal pressure, and no load is applied to the tire, this is referred to as the standard condition.

[0013] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire cross-section (hereinafter referred to as the reference cross-section) obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the distance between the left and right beads is set to match the distance between the beads in a tire mounted on a standard rim.

[0014] A genuine rim refers to a rim defined 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 all considered genuine rims.

[0015] The normal internal pressure means the internal pressure defined in the standard on which the tire depends. The "maximum air pressure" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are the normal internal pressures.

[0016] The normal load means the load defined in the standard on which the tire depends. The "maximum load capacity" in the JATMA standard, the "maximum value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are the normal loads.

[0017] In the present invention, the "claimed section width" and the "claimed aspect ratio" are the "claimed section width" and the "claimed aspect ratio" included in the "tire nomenclature" defined in JIS D4202 "Automobile Tires - Nomenclature and Dimensions".

[0018] In the present invention, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of sidewall portions. The central portion of the tread portion is also referred to as the crown portion. The end portion of the tread portion is also referred to as the shoulder portion. The boundary portion between the tread portion and the sidewall portion is also referred to as the buttress.

[0019] In the present invention, among the elements constituting the tire, the loss tangent (tanδ) of the element made of crosslinked rubber is measured in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial strain = 10% Dynamic strain = ±1% Frequency = 10 Hz [[ID=​​Temperature = 30°C In this measurement, the test piece (length 20 mm × width 4 mm × thickness 1 mm) is sampled from the tire. The length direction of the test piece is made to coincide with the circumferential direction of the tire. When the test piece cannot be sampled from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as rubber sheet) obtained by pressurizing and heating the rubber composition used for forming the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the loss tangent is represented by the loss tangent at 30°C.

[0020] In the present invention, the groove portion of the tread surface is also referred to as the sea surface, and the portion other than the groove is also referred to as the land surface. The land / sea ratio means the ratio of the total area of the land surface to the total area of the tread surface including the sea surface. The land / sea ratio is obtained based on the developed view of the tread surface. The land / sea ratio of the tire used for sports driving on a circuit or the like is set to 65% or more.

[0021] [Summary of Embodiments of the Present Invention] [Configuration 1] A tire according to one aspect of the present invention comprises a pair of beads, a carcass spanning between the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass, wherein the outer surface of the tire comprises a tread surface that contacts the road surface and a pair of side surfaces connected to the tread surface, and the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 92% of the normal internal pressure, and a load of 70% of the normal load is applied to the tire, thereby bringing the tire into contact with a plane, and the tread corresponding to the contact edge of the tire's contact surface. The position on the tread surface is the reference contact position, the axial distance from the equatorial plane is 60% of the axial distance from the equatorial plane to the reference contact position, the position on the tread surface is the inclination confirmation position, in the meridional cross section of the tire, the angle made with the axial direction by the tangent to the contour line of the tread surface at the inclination confirmation position is 2.5 degrees or more and 3.5 degrees or less, and the ratio of the equatorial contact length measured along the equatorial plane to the reference contact length at a position corresponding to 60% of the contact width of the contact surface is the shape index F60, and the shape index F60 is 1.00 or more and 1.20 or less.

[0022] By shaping the tire in this way, a flat tread surface is formed, and the force generated in the opposite direction to the turning direction at the contact patch formed by this tread surface in contact with the road surface is effectively suppressed. In this tire, the flat tread surface can efficiently contribute to the generation of cornering force. This tire can generate greater cornering force. This tire can contribute to improved turning performance.

[0023] [Configuration 2] Preferably, in the tire described in [Configuration 1] above, the contour line of the tread surface in the meridional cross-section includes a plurality of arcs, wherein the plurality of arcs include a first arc centered on the equatorial plane and a pair of second arcs located axially outward from the first arc and connected to the first arc, and the ratio of the radius of the first arc to the radius of the second arcs is 2.00 or more and 4.00 or less. By shaping the tire in this way, a flatter tread surface is created, and the generation of forces in the opposite direction to the turning direction at the contact patch is more effectively suppressed. This tire 2 can generate greater cornering force.

[0024] [Configuration 3] Preferably, in the tire described in [Configuration 2] above, the ratio of the length of the second arc to the length of the first arc is 0.80 or more and 1.00 or less. By shaping the tire in this way, a flatter tread surface is created, and the generation of forces in the opposite direction to the turning direction at the contact patch is more effectively suppressed. This tire 2 can generate greater cornering force.

[0025] [Structure 4] Preferably, in the tire described in any one of the above configurations [Configuration 1] to [Configuration 4], the ratio of the equatorial contact length measured along the equatorial plane to the reference contact length at a position corresponding to 80% of the contact width of the contact surface is the shape index F80, and the shape index F80 is 1.25 or more and 1.45 or less. By aligning the tire in this way, the wear energy within the contact patch is equalized, thus suppressing uneven wear. This tire effectively enhances cornering force while maintaining good resistance to uneven wear.

[0026] [Composition 5] Preferably, in the tire described in any one of the above-mentioned configurations [Configuration 1] to [Configuration 5], the nominal cross-sectional width of the tire is 215 mm or more, and the nominal aspect ratio is 55% or less. By shaping the tire in this way, the flat tread surface of this tire can efficiently contribute to the generation of cornering force. This tire can generate greater cornering force. This tire can contribute to improved turning performance.

[0027] [Details of the Embodiments of the Invention] Figure 1 shows a part of a tire 2 according to the first embodiment of the present invention. This tire 2 is a pneumatic tire for a passenger car. Figure 1 shows a portion of the cross-section of tire 2 (hereinafter referred to as the meridian cross-section) along the plane containing the rotation axis of tire 2. In Figure 1, the left-right direction is the axial direction of tire 2, and the up-down direction is the radial direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the circumferential direction of tire 2. The dashed line CL represents the equatorial plane of tire 2. In Figure 1, tire 2 is mounted on rim R (regular rim). Air is filled inside tire 2, and the internal pressure of tire 2 is adjusted.

[0028] In Figure 1, the position indicated by the symbol PC is the intersection of the outer surface 2G of tire 2 (specifically, the tread surface, which will be described later) and the equatorial plane. Intersection PC is the equator of tire 2. If a groove is located on the equatorial plane, the equatorial PC is determined based on a virtual outer surface obtained by assuming the absence of a groove. The equatorial PC is the radial outer edge of tire 2.

[0029] In Figure 1, the position indicated by the symbol PW is the axial outer end of tire 2 (hereinafter referred to as outer end PW). If there are decorations such as patterns or letters on the outer surface, outer end PW is determined based on a hypothetical outer surface obtained by assuming there are no decorations. The axial distance from the first outer edge PW to the second outer edge PW obtained under normal conditions is the cross-sectional width of tire 2 (see JATMA, etc.). The outer edge PW is also called the maximum width position. The maximum width position is the position where tire 2 exhibits its maximum width. The maximum width obtainable under normal conditions is the cross-sectional width mentioned above.

[0030] In Figure 1, the position indicated by the symbol PT is the toe of tire 2. The toe PT is the boundary between the outer surface 2G and the inner surface 2N of tire 2.

[0031] This tire 2 comprises a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, a pair of chafers 18, and an inner liner 20.

[0032] The tread 4 is made of cross-linked rubber. The tread 4 makes contact with the road surface at its tread surface 22. The tread 4 has a tread surface 22 that makes contact with the road surface. Grooves 24 are cut into the tread 4. The tread 4 is located radially outward of the carcass 12. The tread surface 22 is part of the outer surface 2G of the tire 2. The side surface 26 is continuous with the tread surface 22. The outer surface 2G of the tire 2 comprises the tread surface 22 and a pair of side surfaces 26. The tread surface 22 has an equatorial PC. Each side surface 26 has a maximum width position PW. The outer surface 2G includes the equatorial PC and the maximum width position PW.

[0033] The tread 4 of this tire 2 comprises a cap portion 28 and a base portion 30. The cap portion 28 includes a tread surface 22. The cap portion 28 is made of cross-linked rubber with consideration for wear resistance and grip performance. The base portion 30 is located radially inward of the cap portion 28. The entire base portion 30 is covered by the cap portion 28. The base portion 30 is made of low-heat-generating cross-linked rubber. Although not indicated by a reference numeral, the element between the cap portion 28 and the sidewall 6 is a wing. The cap portion 28 and the sidewall 6 are joined via the wing.

[0034] In this tire 2, it is preferable that the loss tangent Ltc of the cap portion 28 at 30°C is 0.25 or higher. The cap portion 28 can contribute to improving grip performance. In particular, in sports driving on circuits, etc., this cap portion 28 can effectively contribute to increasing cornering force. From this viewpoint, a higher loss tangent Ltc is preferable, so no preferred upper limit is set.

[0035] In this tire 2, it is preferable that the loss tangent Ltb of the base portion 30 at 30°C is 0.11 or less. The base portion 30 contributes to reducing rolling resistance. From this viewpoint, a lower loss tangent Ltb is preferable, so no preferred lower limit is set.

[0036] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 is located axially outward of the carcass 12. The sidewall 6 is made of cross-linked rubber with cut resistance in mind. The sidewall 6 forms part of the side surface 26.

[0037] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is in contact with the rim R. The clinch 8 is made of cross-linked rubber with wear resistance in mind. The clinch 8 forms part of the bead.

[0038] Each bead 10 is located axially inward of the clinch 8. The bead 10 is located radially inward of the sidewall 6. The bead 10 comprises a core 32 and an apex 34. The core 32 extends circumferentially. Although not shown, the core 32 includes a steel bead wire. The apex 34 is located radially outward of the core 32. The apex 34 tapers radially outward. The apex 34 is made of cross-linked rubber with high rigidity.

[0039] The carcass 12 is located inside the tread 4, a pair of sidewalls 6, and a pair of clinches 8. The carcass 12 spans between a pair of beads 10, that is, between the first bead 10 and the second bead 10. The carcass 12 includes at least one carcass ply 36.

[0040] The carcass 12 of the tire 2 shown in Figure 1 is composed of two carcass plies 36. Although not shown, each carcass ply 36 contains numerous parallel carcass cords. These carcass cords intersect the equatorial plane. The carcass 12 of this tire 2 has a radial structure.

[0041] Of the two carcass plies 36, the carcass ply 36 located radially inward on the inside of the tread 4 is the first carcass ply 38. The carcass ply 36 located radially outward from the first carcass ply 38 on the inside of the tread 4 is the second carcass ply 40.

[0042] The first carcass ply 38 includes a first ply body 38a and a pair of first folded portions 38b. The first ply body 38a spans between a pair of beads 10. Each first folded portion 38b is connected to the first ply body 38a and is folded back axially from the inside to the outside on each bead 10.

[0043] The second carcass ply 40 includes a second ply body 40a and a pair of second folded portions 40b. The second ply body 40a spans between the pair of beads 10. Each second folded portion 40b is connected to the second ply body 40a and is folded back axially from the inside to the outside on each bead 10.

[0044] In this tire 2, the end of the first folded portion 38b is located radially outward from the maximum width position PW. The end of the second folded portion 40b is located radially inward from the maximum width position PW. The end of the second folded portion 40b is located radially between the outer end of the apex 34 and the core 32. The second folded portion 40b is located axially inward of the first folded portion 38b. The end of the second folded portion 40b is sandwiched between the apex 34 and the first folded portion 38b.

[0045] The carcass 12 shown in Figure 1 has a high turn-up (HTU) structure. There are no particular restrictions on the structure of the carcass 12 in this tire 2. The carcass 12 may have an ultra-high turn-up (U-HTU) structure or a low turn-up (LTU) structure. The structure of the carcass 12 is determined appropriately according to the specifications of the tire 2.

[0046] In this tire 2, the carcass cords are covered with a topping rubber (hereinafter referred to as the carcass cord coating layer). Examples of elastomer compositions that can be used for the carcass cord coating layer include rubber compositions and thermoplastic elastomer layers.

[0047] When the elastomer composition is a rubber composition, examples of rubber components include isoprene-based rubber, butadiene-based rubber, styrene-butadiene rubber, nitrile rubber, and butyl rubber. Among these, isoprene-based rubber is preferred from the viewpoint of good adhesion to the cord. When the elastomer composition is a thermoplastic elastomer composition, examples of elastomer components include thermoplastic polyurethane, styrene-butadiene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and other block copolymers.

[0048] The elastomer composition is not particularly limited in terms of components other than the rubber component and the elastomer component, but may contain 40 to 70 parts by mass of fillers such as inorganic fillers such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar, and poorly dispersible fillers; 1 to 10 parts by mass of plasticizers such as oil, resin, and liquid polymer; 1 to 4 parts by mass of antioxidants; 0.5 to 2.0 parts by mass of stearic acid; 4 to 10 parts by mass of zinc oxide; 0.5 to 4.0 parts by mass of processed tablets such as metal carboxylate salts; 1.0 to 5.0 parts by mass of thermosetting resin; 3 to 8 parts by mass of sulfur; and 0.5 to 3.0 parts by mass of vulcanization accelerators. Here, "parts by mass" refers to parts by mass per 100 parts by mass of the rubber component or the elastomer component.

[0049] Furthermore, from a life cycle assessment perspective, the carcass cord coating layer described above may also use natural rubber, rice husk-derived silica, lignin-derived fillers and antioxidants, plasticizers obtained by refining waste cooking oil, etc.

[0050] In this tire 2, organic fiber cords formed from organic fibers are used as carcass cords. Examples of organic fibers include polyester, polyamide, and cellulose. These may also be synthetic fibers or biomass-derived fibers. Furthermore, from the perspective of life cycle assessment, it is preferable that they are derived from recycled or recycled materials. These fibers may also be formed from a single component of synthetic fibers, biomass fibers, or recycled / recycled fibers, and may be hybrid cords formed by twisting these together, cords using multifilaments formed by combining the respective filaments, or cords having a chemical structure in which each component is chemically bonded.

[0051] Examples of polyester cords include polyethylene terephthalate (PET) cord, polyethylene naphthalate (PEN) cord, and polyethylene furanoate (PEF). Compared to other polyester cords, PEF may be used because it has superior air permeability resistance and is good at maintaining air pressure inside the tire. Alternatively, a hybrid cord may be used in which a portion of the polyester cord is replaced with a cord made of other organic fibers such as polyamide fibers.

[0052] When the polyester cord is a biomass-derived polyester cord, biomass PET cords using biomass-derived terephthalic acid or ethylene glycol, or biomass PEFs using biomass-derived frangic acid, can be suitably used.

[0053] The aforementioned biomass polyester cord can be obtained by converting it from bioethanol, furfurals, carenes, cymenes, terpenes, etc., or by converting it from various plant and animal-derived compounds, or by directly producing biomass terephthalic acid, biomass ethylene glycol, etc., through fermentation from microorganisms.

[0054] Examples of polyamide codes include aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides.

[0055] Aliphatic polyamides are polyamides that have a backbone in which straight carbon chains are linked by amide bonds, and examples include nylon 4 (PA4), nylon 410 (PA410), nylon 6 (PA6), nylon 66 (PA66), nylon 610 (PA610), nylon 1010 (PA1010), nylon 1012 (PA1012), and nylon 11 (PA11). Among these, nylon 4, nylon 410, nylon 610, nylon 10, nylon 1010, and nylon 11 are particularly easy to obtain from partially or completely biomass-derived materials.

[0056] As nylon 6 and nylon 66, in addition to conventionally synthesized caprolactam obtained by ring-opening polymerization, hexamethylenediamine and adipic acid obtained by condensation polymerization, it is also possible to produce biocaprolactam, bioadipic acid, or biohexamethylenediamine using bio-derived cyclohexane as a starting material, and use nylon 6 or nylon 66 made from these. Furthermore, the aforementioned bio-raw materials may be obtained from sugars such as glucose. These nylon 6 and nylon 66 are expected to have the same strength as those conventionally used.

[0057] A typical example of nylon 4 is one obtained by converting glutamic acid derived from bio-fermentation into γ-aminobutyric acid, followed by 2-pyrrolidone, but it is not limited to this. Nylon 4 has good thermal and mechanical stability and is easy to design as a polymer structure, so it can be suitably used to improve the performance and strength of tires.

[0058] Nylon 410, nylon 610, nylon 1010, nylon 1012, nylon 11, etc., can be obtained using ricinoleic acid, which is derived from castor oil (Ricinus chinensis), as a raw material. Specifically, nylon 410, nylon 610, and nylon 1010 can be obtained by condensation polymerization of sebacic acid, dodecanediic acid, and an arbitrary diamine compound obtained from castor oil, and nylon 11 can be obtained by condensation polymerization of 11-aminoundecanoic acid obtained from castor oil.

[0059] Semi-aromatic polyamides are polyamides that have an aromatic ring structure in part of their molecular chain, and examples include nylon 4T (PA4T), nylon 6T (PA6T), and nylon 10T (PA10T).

[0060] Nylon 4T, Nylon 6T, and Nylon 10T can be obtained by condensation polymerization using terephthalic acid as the dicarboxylic acid and a diamine compound with any number of carbon atoms. It is also possible to obtain these nylon materials using the aforementioned biomass-derived terephthalic acid. Because these materials have a rigid cyclic structure within their molecular chains, they exhibit superior properties such as heat resistance.

[0061] Furthermore, as examples of the aliphatic polyamides and semi-aromatic polyamides mentioned above, we can cite polyamide 5X (where X is the number of carbon atoms derived from the dicarboxylic acid, and is an integer or T represents terephthalic acid) obtained by polymerizing lysine-derived 1,5-pentanediamine with dicarboxylic acids.

[0062] All-aromatic polyamides are polyamides having a skeleton in which aromatic rings are connected by amide bonds, and examples include poly(p-phenylene terephthalamide). Like the aliphatic polyamides and semi-aromatic polyamides mentioned above, all-aromatic polyamides may also be obtained by bonding biomass-derived terephthalic acid with phenylenediamine.

[0063] Examples of cellulose fibers include rayon, polynosic, cupro, acetate, lyocell, and modal, which are manufactured from plant materials such as wood pulp. These cellulose fibers are preferable because, in addition to being carbon neutral in their raw materials, they are biodegradable and do not emit harmful gases when incinerated after use, thus possessing excellent environmental performance. Among the above, rayon, polynosic, and lyocell are particularly preferred due to their balance of process efficiency, environmental friendliness, and mechanical strength.

[0064] Furthermore, the aforementioned cords may be recycled cords obtained by recovering and refining used items such as beverage bottles and clothing, regardless of whether they are synthetic or biomass-derived, and then respinning them.

[0065] The cords described above may be formed by twisting together one or more filaments. For example, two 1100 dsitex multifilaments are combined (in other words, 1100 / 2 dsitex), twisted 48 times / 10cm, and then these two under-twisted cords are combined and twisted the same number of times in the opposite or same direction as the under-twist. Alternatively, two 1670 dsitex multifilaments are combined (in other words, 1670 / 2 dsitex), twisted 40 times / 10cm, and then these two under-twisted cords are combined and twisted.

[0066] As mentioned above, the carcass cord is covered with a carcass cord coating layer. From the viewpoint of ensuring good adhesion with the carcass cord coating layer, it is preferable that the carcass cord is treated with an adhesive layer beforehand. Known adhesive layers can be used, for example, treatment with resorcinol-formaldehyde-rubber latex (RFL), epoxy treatment with an adhesive composition containing sorbitol polyglycidyl ether and blocked isocyanate followed by RFL treatment, or treatment with an adhesive composition containing a halohydrin compound, a blocked isocyanate compound and rubber latex.

[0067] Resorcinol-formaldehyde-rubber latex (RFL) is, for example, an adhesive composition containing natural rubber and / or synthetic rubber latex and a cocondensate of phenol-formaldehyde and resorcinol, as described in Japanese Patent Publication No. 48-11335. Such an adhesive composition can be produced, for example, by a manufacturing method that includes the steps of condensing phenol and formaldehyde in the presence of an alkaline catalyst, copolymerizing an aqueous phenol-formaldehyde resin solution with resorcinol, and mixing the resulting phenol-formaldehyde-resorcinol resin solution with latex rubber.

[0068] Examples of synthetic rubber latex include butadiene polymer latex, styrene / butadiene copolymer latex, isoprene polymer latex, butadiene / acrylonitrile copolymer latex, butadiene / vinylpyridine polymer latex, and butadiene / vinylpyridine / styrene copolymer latex.

[0069] The adhesive layer consisting of the above-mentioned resorcinol-formaldehyde-rubber latex (RFL) can be formed by applying RFL adhesive (such as by dipping the above-mentioned cord in RFL solution). The above-mentioned RFL adhesive is usually applied after twisting to obtain the fiber cord, but it may also be applied before or during twisting.

[0070] The composition of the above RFL adhesive is not particularly limited and may be selected as appropriate, but it is preferably a composition containing 0.1 to 10% by mass of resorcinol, 0.1 to 10% by mass of formalin, and 1 to 28% by mass of latex, and more preferably a composition containing 0.5 to 3% by mass of resorcinol, 0.5 to 3% by mass of formalin, and 10 to 25% by mass of latex.

[0071] Examples of heating methods in the heat treatment include drying the cord to which the RFL adhesive composition is attached at 100-250°C for 1-5 minutes, followed by further heat treatment at 150-250°C for 1-5 minutes. Preferably, the heat treatment conditions after drying are 180-240°C for 1-2 minutes.

[0072] The adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate is not particularly limited as long as it contains sorbitol polyglycidyl ether and blocked isocyanate. In particular, a composition containing an epoxy compound of sorbitol polyglycidyl ether having a chlorine content of 9.6% by mass or less and a blocked isocyanate is preferred.

[0073] Examples of sorbitol polyglycidyl ethers include sorbitol diglycidyl ether, sorbitol triglycidyl ether, sorbitol tetraglycidyl ether, sorbitol pentaglycidyl ether, sorbitol hexaglycidyl ether, or mixtures thereof, and may also include sorbitol monoglycidyl ether. Sorbitol polyglycidyl ether has a large number of epoxy groups in one molecule and can form a highly cross-linked structure.

[0074] The chlorine content of sorbitol polyglycidyl ether is preferably 9.6% by mass or less, more preferably 9.5% by mass or less, even more preferably 9.4% by mass or less, and particularly preferably 9.3% by mass or less. The lower limit of the chlorine content is not particularly limited, and is, for example, 1% by mass or more. In this disclosure, the chlorine content of sorbitol polyglycidyl ether is defined as JIS This can be determined by methods such as those described in K 7243-3.

[0075] The chlorine content of sorbitol polyglycidyl ether can be reduced by reducing the amount of epichlorohydrin used in the synthesis of epoxy compounds, among other things.

[0076] Blocked isocyanates are compounds produced by the reaction of an isocyanate compound with a blocking agent, and are temporarily inactivated by a group derived from the blocking agent. When heated at a predetermined temperature, the group derived from the blocking agent dissociates, generating an isocyanate group.

[0077] Examples of isocyanate compounds include those having two or more isocyanate groups in their molecule. Examples of diisocyanates having two isocyanate groups include hexamethylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, phenylene diisocyanate, tolylene diisocyanate, trimethylhexamethylene diisocyanate, metaphenylene diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, diphenylpropane diisocyanate, biphenyl diisocyanate, and their isomers, alkyl-substituted compounds, halides, hydrogenated compounds to the benzene ring, etc. In addition, triisocyanates having three isocyanate groups, tetraisocyanates having four isocyanate groups, and polymethylene polyphenyl polyisocyanate, etc. These isocyanate compounds can be used individually or in combination of two or more. Among these, tolylene diisocyanate, metaphenylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and polymethylene polyphenyl polyisocyanate are preferred.

[0078] Examples of blocking agents include lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; phenol-based agents such as phenol, cresol, resorcinol, and xylenol; alcohol-based agents such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and benzyl alcohol; oxime-based agents such as formamidexime, acetaldehydexime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexanone oxime; and active methylene-based agents such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone. Among these, lactam-based, phenol-based, and oxime-based blocking agents are preferred.

[0079] In the adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate, the content of the blocked isocyanate is preferably 50 parts by mass or more, more preferably 200 parts by mass or more, per 100 parts by mass of sorbitol polyglycidyl ether. The upper limit is preferably 500 parts by mass or less, more preferably 400 parts by mass or less.

[0080] The adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate may optionally contain the following components: for example, epoxy compounds other than sorbitol polyglycidyl ether, resins copolymerizable with sorbitol polyglycidyl ether, curing agents other than blocked isocyanates, organic thickeners, antioxidants, light stabilizers, adhesion enhancers, reinforcing agents, softeners, colorants, leveling agents, flame retardants, and antistatic agents.

[0081] Examples of epoxy compounds other than sorbitol polyglycidyl ether include glycidyl ethers such as ethylene glycol glycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, novolac glycidyl ether, and brominated bisphenol A diglycidyl ether; glycidyl esters such as hexahydrophthalate glycidyl ester and dimer acid glycidyl ester; triglycerides Examples include glycidylamines such as glycidyl isocyanurate, glycidylhindantoin, tetraglycidyldiaminodiphenylmethane, triglycidylparaaminophenol, triglycidylmetaaminophenol, diglycidylaniline, diglycidyltoluidine, tetraglycidylmetaxylenediamine, diglycidyltribromaniline, and tetraglycidylbisaminomethylcyclohexane; and alicyclic or aliphatic epoxides such as 3,4-epoxycyclohexylmethylcarboxylate, epoxidized polybutadiene, and epoxidized soybean oil.

[0082] Treatment with the adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate includes treatments performed to adhere the various components contained in RFL to the cord, and, if necessary, subsequent heat treatments.

[0083] Any method of application can be used, such as coating with a roller, spraying from a nozzle, or immersion in a bath solution (adhesive composition). From the viewpoint of uniform application and removal of excess adhesive, application by immersion is preferred.

[0084] Furthermore, to adjust the amount of material adhering to the cord, additional methods such as squeezing with a pressure roller, scraping with a scraper, blowing with compressed air, suction, and beating with a beater may be employed.

[0085] The amount adhering to the cord is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and also preferably 3.0% by mass or less, more preferably 2.5% by mass or less. The amount of adhesive adhering to the cord is the amount of solid content in the RFL adhesive adhering to 100 parts by mass of the cord.

[0086] The total solid content concentration of the adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate is preferably 0.9% by mass or more, more preferably 14% by mass or more, and also preferably 29% by mass or less, more preferably 23% by mass or less.

[0087] In addition to resorcinol, formalin, and rubber latex, the adhesive composition containing the above-mentioned sorbitol polyglycidyl ether and blocked isocyanate may also contain vulcanization modifiers, zinc oxide, antioxidants, defoaming agents, etc.

[0088] Examples of heating methods in the heat treatment include drying the reinforcing material to which the RFL adhesive composition is attached at 100-250°C for 1-5 minutes, and then further heat-treating it at 150-250°C for 1-5 minutes. Preferably, the heat treatment conditions after drying are 180-240°C for 1-2 minutes.

[0089] The adhesive composition containing the above-mentioned halohydrin compound, blocked isocyanate compound, and rubber latex is not particularly limited as long as it contains these components, but an adhesive composition containing the halohydrin compound, blocked isocyanate compound, and rubber latex, and not containing resorcinol and formaldehyde, is preferred.

[0090] Examples of halohydrin compounds include compounds obtained by reacting polyol compounds with epihalohydrin compounds (halohydrin ethers). Polyol compounds are compounds having two or more hydroxyl groups in their molecule. Examples include glycols such as ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; hydroxyl acids such as erythritol, xylitol, sorbitol, and tartaric acid; glyceric acid, glycerin, diglycerin, polyglycerin, trimethylolpropane, trimethylolethane, and pentaerythritol. Examples of epihalohydrin compounds include epichlorohydrin and epibromohydrin.

[0091] Examples of halohydrin compounds include fluoroalcohol compounds, chlorohydrin compounds, bromohydrin compounds, and iodohydrin compounds. Among these, halogenated sorbitol and halogenated glycerol are preferred.

[0092] The halogen content in 100% by mass of the halohydrin compound is preferably 5.0 to 15.0% by mass, more preferably 7.0 to 13.0% by mass, and even more preferably 9.0 to 12.0% by mass.

[0093] Examples of blocked isocyanate compounds include those similar to the blocked isocyanates mentioned above. Similarly, examples of rubber latex include those similar to the rubber latex mentioned above.

[0094] The adhesive composition containing the above-mentioned halohydrin compound, blocked isocyanate compound, and rubber latex preferably contains 10.0 to 30.0 parts by mass of the halohydrin compound, 10.0 to 30.0 parts by mass of the blocked isocyanate compound, and 80.0 to 240.0 parts by mass of rubber latex. Furthermore, the adhesive composition does not contain resorcinol or formaldehyde.

[0095] An adhesive layer comprising an adhesive composition containing the above-mentioned halohydrin compound, blocked isocyanate compound, and rubber latex is formed on the surface of the cord using the adhesive composition. The adhesive layer is formed by, for example, dipping, brushing, casting, spraying, roll coating, knife coating, etc.

[0096] The belt 14 is located radially inward of the tread 4. The belt 14 is laminated on the carcass 12. The aforementioned equatorial plane intersects the belt 14 at the center of the axial width of the belt 14. In this tire 2, the axial width of the belt 14 is between 70% and 90% of the cross-sectional width of tire 2.

[0097] The belt 14 comprises at least one layer 42. The belt 14 may be composed of multiple layers 42 stacked radially. The belt 14 of this tire 2 comprises two layers 42 stacked radially. The layer 42 located radially outward of the second ply body 40a and stacked on the second ply body 40a is the first layer 44. The layer 42 located radially outward of the first layer 44 and stacked on the first layer 44 is the second layer 46. The belt 14 comprises the first layer 44 and the second layer 46.

[0098] As shown in Figure 1, the edge of the second layer 46 is located radially inward from the edge of the first layer 44. The second layer 46 is narrower than the first layer 44. The length from the edge of the second layer 46 to the edge of the first layer 44 is between 3 mm and 10 mm. The axial width of the belt 14 is expressed by the axial width of the wider first layer 44.

[0099] Although not shown in the diagram, the first layer 44 and the second layer 46 each contain numerous parallel belt cords. These belt cords are covered with topping rubber (hereinafter referred to as the belt cord covering layer). Each belt cord is inclined with respect to the equatorial plane. The belt cords are made of steel cord.

[0100] In this tire 2, it is preferable that the steel cord included in the belt 14 is composed of an N×M structure, where M of N filaments are combined. Here, N and M are integers of 1 or more, and it may also be a 1×1 structure in which single-wire steel cords are arranged side by side. When N is 1, it is preferable to use filaments that have been bent in the longitudinal direction. When N is 2 or more, it is preferable that the N filaments are twisted together. On the other hand, when M is 2 or more, it is preferable that the N filaments that have been combined in advance are twisted together. From the viewpoint of the belt cord coating layer penetrating into the inside of the cord and obtaining good adhesion, it is preferable to use some of the filaments that have been bent as described above.

[0101] The steel cord may be a monofilament structure made by arranging single-strand cords, an N×M structure made by twisting multiple filaments together, a layered structure such as an N+M structure or an N+M+R structure, or a multi-strand structure made by further twisting bundles or twists of multiple filaments together (N, M, and R are all integers).

[0102] The diameter of the filament is preferably 0.10 mm or more and 0.50 mm or less. If M is 2 or more, the diameter of the circumscribed circle of the twisted cord is preferably 0.2 mm or more and 1.0 mm or less. In the case of a 1x1 structure consisting of a single-wire cord, the cross-sectional shape perpendicular to the longitudinal direction of the cord may be flattened. If the cross-section is flattened, the simple average of the minor and major axes is treated as the outer diameter.

[0103] The belt 14 has multiple steel cords arranged in the width direction. There are no particular limitations on the number of cords arranged in the width direction, but the product of the number of cords arranged in the width direction over a 5 cm area and the cross-sectional area of ​​the cords should be between 4.5 and 15.0 mm². 2 It is preferable that it be within the range of / 5cm.

[0104] Furthermore, the steel cord may be plated on its surface, including copper and zinc elements, from the viewpoint of adhesion. Other elements that are preferably located between copper and zinc in terms of ionization tendency include, for example, cobalt, nickel, tin, antimony, bismuth, and the like.

[0105] As mentioned above, in this tire 2, the belt cords are covered with a belt cord coating layer. Preferably, these belt cords are covered with a belt cord coating layer formed from an elastomer composition. Examples of elastomer compositions that can be used for the belt cord coating layer include rubber compositions and thermoplastic elastomer layers.

[0106] When the elastomer composition is a rubber composition, examples of rubber components include isoprene-based rubber, butadiene-based rubber, styrene-butadiene rubber, nitrile rubber, and butyl rubber. Among these, isoprene-based rubber is preferred from the viewpoint of good adhesion to steel cords. When the elastomer composition is a thermoplastic elastomer composition, examples of elastomer components include thermoplastic polyurethane, styrene-butadiene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and other block copolymers.

[0107] The elastomer composition is not particularly limited in terms of components other than the rubber and elastomer components, but may contain 40 to 70 parts by mass of fillers such as inorganic fillers such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar, and poorly dispersible fillers; 1 to 10 parts by mass of plasticizers such as oil, resin, and liquid polymer; 1 to 4 parts by mass of antioxidants; 0.5 to 2.0 parts by mass of stearic acid; 5 to 12 parts by mass of zinc oxide; 0.5 to 4.0 parts by mass of processed tablets such as metal carboxylate salts; 0.5 to 3.0 parts by mass of adhesive aids such as cobalt compounds; 1.0 to 5.0 parts by mass of thermosetting resin; 4 to 8 parts by mass of sulfur; and 0.5 to 3.0 parts by mass of vulcanization accelerators. Here, "parts by mass" refers to parts by mass per 100 parts by mass of the rubber or elastomer component.

[0108] Furthermore, from a life cycle assessment perspective, the belt cord coating layer may also use natural rubber, silica derived from rice husks, fillers and antioxidants derived from lignin, plasticizers obtained by refining waste cooking oil, etc.

[0109] The band 16 is located radially between the tread 4 and the belt 14. The band 16 is laminated on the belt 14. The end of band 16 is located axially outward from the end of belt 14. The distance from the end of belt 14 to the end of band 16 is between 3 mm and 7 mm. Although not shown, band 16 includes a helically wound band cord. The band cord extends substantially circumferentially. In detail, the angle that the band cord makes with respect to the circumferential direction is 5° or less. Band 16 has a jointless structure. The band cord is an organic fiber cord. This band cord uses the same type of cord as the carcass cord mentioned earlier. The band cord is covered with topping rubber. This topping rubber, i.e., the coating layer of the band cord, uses the same elastomer composition and various compounding agents as the carcass cord coating layer contained in the carcass 12 described above. From the viewpoint of life cycle assessment, natural rubber, rice husk-derived silica, lignin-derived fillers and antioxidants, plasticizers obtained by refining waste cooking oil, etc. may also be used in this coating layer.

[0110] Band 16 comprises a full band 48 and a pair of edge bands 50. The full band 48 is stacked on the belt 14. The full band 48 covers the entire belt 14. Each end of the full band 48 is located axially outward from the end of the belt 14. A pair of edge bands 50 are positioned axially separated from each other across the equatorial plane. Each edge band 50 is stacked on the full band 48. The edge bands 50 cover the edges of the full band 48. This band 16 may be composed of a full band 48. This band may be composed of two full bands 48 stacked radially. This band 16 may be composed of a pair of edge bands 50.

[0111] Each chafer 18 is located radially inward of the bead 10. The chafer 18 is in contact with the rim R. The chafer 18 of this tire 2 consists of cloth and rubber impregnated into this cloth.

[0112] The inner liner 20 is located inside the carcass 12. The inner liner 20 constitutes the inner surface 2N of the tire 2. The inner liner 20 is made of cross-linked rubber with excellent air shielding properties. The inner liner 20 maintains the internal pressure of the tire 2.

[0113] As mentioned above, grooves 24 are cut into the tread 4. The grooves 24 include grooves that extend in the circumferential direction (hereinafter referred to as circumferential grooves 52). In this tire 2, at least three circumferential grooves 52 are carved into the tread 4. In the tread 4 shown in Figure 1, four circumferential grooves 52 are carved into the tread 4. This results in the formation of five land sections 54. Of the four circumferential grooves 52, the circumferential groove 52 located on the outer side in the axial direction is the shoulder circumferential groove 52s. The circumferential groove 52 located on the inner side in the axial direction of the shoulder circumferential groove 52s is the middle circumferential groove 52m. Of the five land sections 54, the land section 54 located on the outer side in the axial direction is the shoulder land section 54s. The land section 54 located axially inward from the shoulder land section 54s is the middle land section 54m. The land section 54 located axially inward from the middle land section 54m is the center land section 54c.

[0114] Figure 2 shows a portion of the outline of the outer surface 2G in the meridional cross-section of tire 2. The outline is represented by a hypothetical outer surface obtained by assuming the absence of grooves, patterns, letters, and other decorations. Although not described in detail here, in this invention, the contour of the outer surface 2G is obtained, for example, by measuring the outer surface shape of the tire 2 in a reference state using a displacement sensor. The contour of this outer surface 2G may also be determined based on the shape of the cavity surface of the mold (not shown) that forms this outer surface 2G of the tire 2.

[0115] In the meridian cross-section, the contour line of the tread surface 22 includes multiple circular arcs aligned in the axial direction. This contour line is composed of multiple circular arcs aligned in the axial direction. Of the multiple arcs, the arc located furthest out in the axial direction is the shoulder arc. In Figure 2, the arrow indicated by the symbol Rh represents the radius of the shoulder arc. The shoulder arc has the smallest radius Rh among the multiple arcs that make up the contour line of the tread surface 22. The contour lines of the tread surface 22 include a pair of shoulder arcs. The contour lines of the side surface 26 are connected to each of the shoulder arcs.

[0116] In Figure 2, the symbol HU represents the outer end of the shoulder arc. This outer end HU is the boundary between the shoulder arc and the contour line of the side surface 26. The symbol SH represents the inner end of the shoulder arc. This inner end SH is the boundary with the arc located axially inward of this shoulder arc (the third arc, described later).

[0117] The contour of the tread surface 22 includes at least three arcs between a pair of shoulder arcs, i.e., between the first shoulder arc and the second shoulder arc (not shown). In the tread surface 22 of this tire 2, the contour includes five arcs between the first shoulder arc and the second shoulder arc.

[0118] Of the five arcs, the arc located in the center in the axial direction is the first arc. In Figure 2, the arrow denoted by Rc represents the radius of the first arc. The first arc passes through the equator PC. Although not shown in the figure, the center of the first arc lies on the equatorial plane. The arc adjacent to the first arc is the second arc. The second arc is located axially outward from the first arc and is connected to it. In Figure 2, the arrow denoted by Rm is the radius of the second arc. The position denoted by CM is the boundary between the first and second arcs. In this tire 2, the second arc is tangent to the first arc at boundary CM. The arc adjacent to the second arc is the third arc. The third arc is located axially outward from the second arc and is connected to it. In Figure 2, the arrow denoted by Rs is the radius of the third arc. The position denoted by MS is the boundary between the second and third arcs. In this tire 2, the third arc is tangent to the second arc at boundary MS. The arc adjacent to the third arc is the aforementioned shoulder arc. As previously stated, the inner end SH of the shoulder arc is the boundary between the third arc and the shoulder arc. In this tire 2, the shoulder arc is tangent to the third arc at boundary SH. The contour of the tread surface 22 includes a first circular arc, a pair of second circular arcs, a pair of third circular arcs, and a pair of shoulder circular arcs. The radius Rm of the second circular arc is smaller than the radius Rc of the first circular arc. The radius Rs of the third circular arc is smaller than the radius Rm of the second circular arc. The radius Rh of the shoulder circular arc is smaller than the radius Rs of the third circular arc.

[0119] In Figure 2, the line LSH is a tangent line that touches the shoulder arc at boundary SH. The line LHU is a tangent line that touches the shoulder arc at boundary HU. The symbol PE is the intersection of tangent line LSH and tangent line LHU. In this invention, this intersection point PE is the reference end of the tread 4. The length indicated by the symbol HWE is the axial distance from the equatorial plane to the reference end PE. In this invention, the axial distance HWE is the reference width of the tread 4. The width of the tread 4 is twice the length of the reference width HWE.

[0120] In Figure 2, the length indicated by the symbol HWCM is the axial distance from the equatorial plane to the boundary CM. The length indicated by the symbol HWMS is the axial distance from the equatorial plane to the boundary MS. In this tire 2, the ratio of the axial distance HWCM to the reference width HWE (HWCM / HWE) is preferably 25% to 35%. The ratio of the axial distance HWMS to the reference width HWE (HWMS / HWE) is preferably 55% to 65%.

[0121] Figure 3 shows the contour of the contact surface of tire 2. In Figure 3, the left-right direction corresponds to the axial direction of tire 2, and the up-down direction corresponds to the circumferential direction of tire 2.

[0122] The contour of the contact surface is obtained using a tire contact surface shape measuring device (not shown) as follows: A load of 70% of the normal load is applied to tire 2 in a standard state, and tire 2 is brought into contact with a plane. At this time, tire 2 is positioned so that its axial direction is parallel to the plane. The camber angle of tire 2 is set to 0 degrees, and the aforementioned load is applied to tire 2 in a direction perpendicular to the plane. Although not described in detail, an image of the contact surface formed by the tire 2 contacting a plane is obtained by a known method. Based on the obtained image of the contact surface, the contour of the contact surface is identified. The contour of the contact surface is obtained by tracing the periphery of the contact surface in the contact surface image. If the periphery of the contact surface is interrupted by a groove, the interrupted portion is connected with a straight line to trace the contour of the contact surface. The contact surface with the contour obtained in this way is used as the contact surface of the tire 2 obtained by applying a load of 70% of the normal load to the tire 2 in a standard state and bringing the tire 2 into contact with a plane. Based on the contour of the obtained contact surface, the shape of the contact surface is analyzed.

[0123] In Figure 3, the position indicated by the symbol GE is the axial outer end of the grounding surface. In this invention, this axial outer end GE is the grounding end. The length indicated by the symbol WC is the grounding width. The grounding width is the axial distance from the first grounding end GE to the second grounding end GE, and is specified on the grounding surface shown in Figure 3.

[0124] In Figure 3, the dashed line LP extending vertically is the straight line corresponding to the equatorial PC of tire 2 at the contact surface. If it is difficult to identify the equatorial PC at the contact surface, the axial center line of the contact width WC is used as the straight line corresponding to this equatorial PC. The double arrow B100 is the length of the intersection line between the plane containing the straight line LP and the contact surface. In this tire 2, the length of this intersection line B100 is the equatorial contact length measured along the equatorial plane at the contact surface.

[0125] In Figure 3, the solid line LE is a straight line passing through the grounding end GE and parallel to the straight line LP. The length indicated by the symbol A100 is the axial distance from the straight line LP to the straight line LE. Distance A100 corresponds to half the grounding width WC. The solid line LX is a straight line located between lines LE and LP, and is parallel to both lines LE and LP. The length indicated by the double arrow AX is the axial distance from line LP to line LX. The double arrow BX is the length of the intersection line between the plane containing line LX and the ground plane. In this invention, this length BX is the contact length at a predetermined position on the contact surface and is referred to as the reference contact length. The ratio of the equatorial contact length B100 to the reference contact length BX (B100 / BX) is the shape index, and the shape of the contact surface is determined by this shape index.

[0126] In this invention, the ratio of distance AX to distance A100 (AX / A100) is set to 60% or 80%. When the ratio (AX / A100) is 60%, length BX represents the contact length at a position corresponding to 60% of the contact width on the contact surface, and this contact length is expressed as the standard contact length B60. The shape index F60 is then expressed as the ratio (B100 / B60) of the equatorial contact length B100 to the standard contact length B60. When the ratio (AX / A100) is 80%, length BX represents the contact length at a position corresponding to 80% of the contact width on the contact surface, and this contact length is expressed as the standard contact length B80. The shape index F80 is then expressed as the ratio (B100 / B80) of the equatorial contact length B100 to the standard contact length B80.

[0127] In Figure 2, the position indicated by the symbol PH is the position on the tread surface 22 corresponding to the contact edge GE shown in Figure 3. In this invention, this position PH is the reference contact position. As shown in Figure 2, in this tire 2, the portion of the tread surface 22 represented by the third arc includes this reference contact position PH. The length indicated by the symbol HWH is the axial distance from the equatorial plane to the reference grounding position PH. In this tire 2, the ratio of the axial distance HWH from the equatorial plane to the reference contact point PH to the reference width HWE of the tread 4 (HWH / HWE) is preferably 75% or more and 90% or less.

[0128] The position indicated by the symbol P60 is a specific position on the tread surface 22. In this invention, position P60 is also referred to as the inclination confirmation position. The length indicated by the symbol HW60 is the axial distance from the equatorial plane to the inclination confirmation position P60. In this invention, the ratio of the axial distance HW60 to the axial distance HWH (HW60 / HWH) is set to 60%. The inclination confirmation position P60 is a position on the tread surface 22 where the axial distance HW60 from the equatorial plane is 60% of the axial distance HWH from the equatorial plane to the reference ground contact position PH. As shown in Figure 2, in this tire 2, the inclination confirmation position P60 is located between boundary CM and boundary MS in the axial direction. In other words, in the contour line of the tread surface 22, the inclination confirmation position P60 is located on the second arc.

[0129] The position indicated by the symbol P80 is a specific position on the tread surface 22. The length indicated by the symbol HW80 is the axial distance from the equatorial plane to the specific position P80. In this invention, the ratio of the axial distance HW80 to the axial distance HWH (HW80 / HWH) is set to 80%. Position P80 is a position on the tread surface 22 where the axial distance HW80 from the equatorial plane is 80% of the axial distance HWH from the equatorial plane to the reference ground contact position PH. As shown in Figure 2, in this tire 2, position P80 is located axially outward from the boundary MS. In other words, in the contour of the tread surface 22, position P80 is located on the third arc. In this tire 2, this position 80 may coincide with the boundary MS, or it may be located axially inward from the boundary MS. When position 80 is located axially inward from the boundary MS, in the contour of the tread surface 22, position P80 is located on the second arc.

[0130] In Figure 2, the solid line denoted by AL is a straight line passing through the equator PC and extending in the axial direction. The straight line denoted by TL60 is the tangent to the contour line of the tread surface 22 at the inclination confirmation position P60. The angle θ is the angle between the straight line AL and the tangent line TL60. In this invention, the angle θ is the angle that the tangent line TL60 to the contour line of the tread surface 22 at the inclination confirmation position P60 makes with respect to the axial direction in the meridian cross-section of the tire 2.

[0131] In sports driving on circuits and other similar environments, it is essential that vehicles can corner at higher speeds. To further increase the cornering force generated during cornering, the inventors used the Finite Element Method (FEM) to investigate the force generation at the contact patch during cornering with a camber angle of -3 degrees and a slip angle of 2 degrees. They discovered that in conventional tires, a force opposite to the direction of cornering is generated on a portion of the contact patch. A force opposite to the direction of cornering reduces the cornering force. Since suppressing the generation of a force opposite to the direction of cornering can further increase the cornering force, the inventors reviewed the relationship between the tread surface contour in the meridional cross-section of the tire and the shape of the contact patch, and have now completed the present invention.

[0132] In this tire 2, in the meridian cross-section, the angle θ that the tangent line TL60 of the contour line of the tread surface 22 makes with respect to the axial direction at the inclination confirmation position P60 is between 2.5 degrees and 3.5 degrees. Since the angle θ is 3.5 degrees or less, a flatter tread surface 22 is formed. Because the tread surface 22 effectively contacts the road surface, a wider contact area is formed. A large cornering force is generated with this tire 2. Since the angle θ is 2.5 degrees or greater, even if tire 2 is mounted on the vehicle with negative camber, wear and damage to the shoulder portion of the vehicle are suppressed. This tire 2 can achieve improved high-speed durability and resistance to uneven wear. When the angle θ exceeds 3.5 degrees, it becomes difficult to create the desired flat tread surface. In this case, the cornering force decreases. If the angle θ is less than 2.5 degrees, when tire 2 is mounted on the vehicle with negative camber, wear and damage are likely to occur on the shoulder portion of the vehicle, and sufficient high-speed durability and resistance to uneven wear cannot be obtained.

[0133] Furthermore, when a load of 70% of the normal load is applied to tire 2 in its standard state, the shape index F60 at the contact surface where tire 2 can be brought into contact with a flat surface is between 1.00 and 1.20. Since the shape index F60 is 1.00 or higher, the contact surface is formed with an appropriate shape and body length without constriction near the center. The tread surface 22 can effectively contribute to the generation of cornering force. Forces acting in the opposite direction to the turning direction are unlikely to occur on this contact surface. A large cornering force is generated in this tire 2. From this viewpoint, it is preferable that the shape index F60 is 1.05 or higher. Since the shape index F60 is 1.20 or less, the bulging of the contact patch in the center is effectively suppressed. Even in this case, the contact patch is composed of a shape with an appropriate length. Forces acting in the opposite direction to the turning direction are unlikely to occur on this contact patch. A large cornering force is generated in this tire 2. From this viewpoint, it is preferable that the shape index F60 is 1.15 or less.

[0134] In this tire 2, the angle θ that the tangent line TL60 of the contour line of the tread surface 22 makes with respect to the axial direction at the inclination confirmation position P60 is between 2.5 degrees and 3.5 degrees. When a load of 70% of the normal load is applied to the tire 2 in its standard state, the shape index F60 at the contact surface where the tire 2 can be brought into contact with a plane is between 1.00 and 1.20. In this tire 2, a flat tread surface 22 is formed, and the contact surface formed by the tread surface 22 in contact with the road surface effectively suppresses the generation of a force in the opposite direction to the turning direction. In this tire 2, the flat tread surface 22 can efficiently contribute to the generation of cornering force. This tire 2 can generate a greater cornering force. This tire 2 can contribute to improved turning performance.

[0135] In this tire 2, the ratio of the radius Rc of the first arc to the radius Rm of the second arc (Rc / Rm) is preferably between 2.00 and 4.00. By setting the ratio (Rc / Rm) to 2.00 or higher, a flatter tread surface 22 is formed. Since the tread surface 22 effectively contacts the road surface, a wider contact patch is formed. This tire 2 generates a large cornering force. From this viewpoint, a ratio (Rc / Rm) of 2.50 or higher is more preferable. By setting the ratio (Rc / Rm) to 4.00 or less, the shape index F60 is prevented from falling below 1.00. In other words, the contact surface is formed with an appropriate shape for the body length without being constricted near the center. From this viewpoint, a ratio (Rc / Rm) of 3.50 or less is more preferable.

[0136] In this invention, the length of the first arc L1 refers to the length from the equator PC to the boundary CM in a circle of radius Rc. The length of the second arc L2 refers to the length from the boundary CM to the boundary MS in a circle of radius Rm. The length of the third arc L3 refers to the length from the boundary MS to the boundary SH in a circle of radius Rs.

[0137] In this tire 2, it is preferable that the ratio of the length of the second arc L2 to the length of the first arc L1 (L2 / L1) is between 0.80 and 1.00. By setting the ratio (L2 / L1) to 0.80 or higher, the boundary CM between the first and second arcs is prevented from being included in the axially outward portion from the position where the ratio (AX / A100) indicates 60% on the contact surface. This prevents the shape index F60 from falling below 1.00. In other words, the contact surface is formed with an appropriate shape in terms of body length without being constricted near the center. From this viewpoint, it is more preferable that this ratio (L2 / L1) is 0.85 or higher. By setting the ratio (L2 / L1) to 1.00 or less, a flatter tread surface 22 is formed. Since the tread surface 22 effectively contacts the road surface, a wider contact patch is formed. This tire 2 generates a large cornering force. From this viewpoint, it is more preferable that this ratio (L2 / L1) is 0.95 or less.

[0138] In this tire 2, a flat tread surface 22 is constructed while considering the generation of forces in the opposite direction to the turning direction in order to increase cornering force. In this tire 2, the portion of the tread surface 22 from the equator PC to the boundary SH is composed of the first arc, the second arc, and the third arc. However, depending on this configuration, there is a concern that the difference between the outer diameter of the crown portion and the outer diameter of the shoulder portion may become large. In this case, the contact length at the shoulder portion becomes shorter, wear is more likely to occur at the crown portion, and resistance to uneven wear decreases. As a result, even though the tire 2 has been tuned to generate higher cornering force, it will not be able to fully perform its function.

[0139] However, in this tire 2, the aforementioned shape index F80 is taken into consideration. Specifically, when a load of 70% of the normal load is applied to the tire 2 in its standard state, and the tire 2 is brought into contact with a flat surface, the shape index F80 at the contact surface is preferably 1.25 or more and 1.45 or less. By setting the shape index F80 to 1.45 or less, the discrepancy between the outer diameter of the crown portion and the outer diameter of the shoulder portion is suppressed, and the contact length at the shoulder portion is configured to an appropriate length. Since the wear energy within the contact surface is equalized, the occurrence of uneven wear is suppressed. In this tire 2, cornering force is effectively increased while maintaining good resistance to uneven wear. From this viewpoint, it is more preferable for the shape index F80 to be 1.40 or less, and even more preferable for it to be 1.35 or less. By setting the shape index F80 to 1.25 or higher, the generation of forces in the opposite direction to the turning direction at the contact patch is more effectively suppressed. In this tire 2, the cornering force is effectively increased. From this viewpoint, a shape index F80 of 1.30 or higher is more preferable.

[0140] When a tire 2 in its standard state is subjected to a load of 70% of its normal load and brought into contact with a flat surface, the ratio of the equatorial contact length B100 to the contact width WC (B100 / WC) at the contact surface of the tire 2 is preferably 0.65 or less. This creates a flat tread surface 22, and the generation of a force opposite to the turning direction at the contact surface formed by this tread surface 22 in contact with the road surface is effectively suppressed. In this tire 2, the flat tread surface 22 can efficiently contribute to the generation of cornering force. This tire 2 can generate a greater cornering force. This tire 2 can contribute to improved turning performance. From this viewpoint, a ratio (B100 / WC) of 0.60 or less is more preferable. A ratio (B100 / WC) of 0.40 or higher is preferable. This equalizes the wear energy within the contact surface, thereby suppressing uneven wear. From this viewpoint, a ratio (B100 / WC) of 0.45 or higher is more preferable.

[0141] In this tire 2, the ratio of the radius Rs of the third arc to the radius Rm of the second arc (Rs / Rm) is preferably between 0.30 and 0.40. By setting the ratio (Rs / Rm) to 0.30 or higher, the discrepancy between the outer diameter of the crown portion and the outer diameter of the shoulder portion is suppressed, and the contact length at the shoulder portion is configured to an appropriate length. Since the wear energy within the contact surface is equalized, the occurrence of uneven wear is suppressed. In this tire 2, cornering force is effectively increased while maintaining good resistance to uneven wear. From this viewpoint, a ratio (Rs / Rm) of 0.33 or higher is more preferable. By setting the ratio (Rs / Rm) to 0.40 or less, the generation of forces opposite to the turning direction at the contact patch is more effectively suppressed. With this tire 2, the cornering force is effectively increased. From this viewpoint, a ratio (Rs / Rm) of 0.37 or less is more preferable.

[0142] In this tire 2, the ratio of the axial distance HWMS from the equatorial plane to the boundary MS to the axial distance HWH from the equatorial plane to the reference contact point PH (HWMS / HWH) is preferably 60% or more and 90% or less. By setting the ratio (HWMS / HWH) to 60% or higher, the discrepancy between the outer diameter of the crown portion and the outer diameter of the shoulder portion is suppressed, and the contact length at the shoulder portion is configured to an appropriate length. Since the wear energy within the contact surface is equalized, the occurrence of uneven wear is suppressed. In this tire 2, cornering force is effectively increased while maintaining good resistance to uneven wear. From this viewpoint, a ratio (HWMS / HWH) of 65% or higher is more preferable, 70% or higher is even more preferable, and 75% or higher is particularly preferable. By setting the ratio (HWMS / HWH) to 90% or less, the generation of forces in the opposite direction to the turning direction at the contact patch is more effectively suppressed. With this tire 2, the cornering force is effectively increased. From this viewpoint, a ratio (HWMS / HWH) of 85% or less is more preferable, and 80% or less is even more preferable.

[0143] As described above, the present invention provides a tire that can achieve improved cornering performance. The present invention is particularly effective for tires with a nominal cross-sectional width of 215 mm or more, a nominal aspect ratio of 55% or less, and a land / sea ratio of 65% or more, specifically for tires used in sports driving on circuits, etc. The tires to which the present invention is applied are preferably those with a nominal section width of 235 mm or more and a nominal aspect ratio of 50% or less, and more preferably those with a nominal section width of 335 mm or more and a nominal aspect ratio of 45% or less. [Examples]

[0144] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0145] [Example 1] A pneumatic tire for passenger cars (tire size = 255 / 40R20) with the basic configuration shown in Figure 1-2 was prepared. The angle θ, radius Rc, ratio (Rc / Rm), ratio (L2 / L1), shape index F60, and shape index F80 were set as shown in Table 1 below.

[0146] [Comparative Example 1-2] Tires for Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the angle θ, radius Rc, ratio (Rc / Rm), ratio (L2 / L1), shape index F60, and shape index F80 were as shown in Table 1 below. Comparative Example 1 is a conventional tire.

[0147] [Grounding shape] The prototype tire was mounted on a rim (size = 20 × 9.0J), the internal pressure was set to 230kPa, and the camber angle was set to 0 degrees. When a load of 5.01kN was applied to the tire, the contact condition was calculated using the finite element method, and the contact shape was obtained. The results are shown in the "Contact Shape" column of Table 1 below.

[0148] [Generation of cornering force] The prototype tire was mounted on a rim (size = 20 × 9.0J), and the internal pressure was set to 230kPa. The force generated at the contact patch during cornering was calculated using the finite element method, with a camber angle of -3 degrees and a slip angle of 2 degrees, to obtain the maximum cornering force. The results are shown in the "Cfmax" column of Table 1 below, using an index where Comparative Example 1 is set to 100. A larger value indicates a greater cornering force.

[0149] [Table 1]

[0150] As shown in Table 1, it has been confirmed that a large cornering force is generated in the examples. It is clear that the tires in the examples can contribute to improved turning performance. From these evaluation results, the advantages of the present invention are clear. [Industrial applicability]

[0151] The technologies described above for improving cornering performance can be applied to various types of tires. [Explanation of symbols]

[0152] 2... Tires 4. Tread 6. Sidewall 10...bead 12...Carcass 14. Belt 16 bands 22...Tread surface 26... Side view 28... Cap section 30...Base section 36...Carcass ply 44...first layer 46...Second layer 48... Full Band 50 Edge Band

Claims

1. A tire comprising a pair of beads, a carcass spanning the pair of beads, a tread located radially outward of the carcass, and a pair of sidewalls located axially outward of the carcass, The outer surface of the tire comprises a tread surface that contacts the road surface and a pair of side surfaces connected to the tread surface. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 92% of the standard internal pressure, and a load of 70% of the standard load is applied to the tire. The position on the tread surface corresponding to the contact edge of the tire's contact surface, obtained by bringing the tire into contact with a flat surface, is the reference contact position. The position on the tread surface where the axial distance from the equatorial plane is 60% of the axial distance from the equatorial plane to the reference ground contact position is the inclination confirmation position. In the meridional cross-section of the tire, the angle that the tangent to the contour line of the tread surface at the inclination confirmation position makes with respect to the axial direction is 2.5 degrees or more and 3.5 degrees or less. In the aforementioned contact surface, the ratio of the equatorial contact length measured along the equatorial plane to the reference contact length at a position corresponding to 60% of the contact width of the contact surface is the shape index F60. The shape index F60 is 1.00 or more and 1.20 or less. tire.

2. The contour line of the tread surface in the meridional cross-section of the tire includes a plurality of arcs, Each of the aforementioned arcs includes a first arc having its center on the equatorial plane and a pair of second arcs located axially outward from the first arc and connected to the first arc. The ratio of the radius of the first arc to the radius of the second arc is 2.00 or more and 4.00 or less. The tire according to claim 1.

3. The ratio of the length of the second arc to the length of the first arc is 0.80 or more and 1.00 or less. The tire according to claim 2.

4. The ratio of the equatorial grounding length measured along the equatorial plane on the grounding surface to the reference grounding length at a position corresponding to 80% of the grounding width of the grounding surface is the shape index F80. The shape index F80 is 1.25 or more and 1.45 or less. The tire according to claim 1.

5. The nominal cross-sectional width of the aforementioned tire is 215 mm or more, and its nominal aspect ratio is 55% or less. The tire according to claim 1 or 2.

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