tire

Abstract

The present invention provides a tire (2) that can effectively reduce rolling resistance and improve wet performance. The tread (4) of the tire (2) includes a base layer (44), an intermediate layer (46) covering the base layer (44), and a crown layer (48) covering the intermediate layer (46). The crown layer 48 includes a tread surface T. The loss tangent of the intermediate layer (46) at 30°C is lower than the loss tangent of the crown layer (48) at 30°C, and the loss tangent of the base layer (44) at 30°C is lower than the loss tangent of the intermediate layer (46) at 30°C. In the reference ground contact surface, the land portion (26) having the longest ground contact length is the longest land portion 26w, the land portion (26) having the shortest ground contact length is the shortest land portion 26n, and the ratio (TL / TS) of the thickness TL of the intermediate layer (46) in the longest land portion 26w to the thickness TS of the intermediate layer (46) in the shortest land portion 26n is greater than 1.0 and less than or equal to 3.5.

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] If low-heat-generating rubber is used for the tread, a tire with low rolling resistance can be obtained. Low-heat-generating rubber is not as good as heat-generating rubber in terms of grip. Therefore, if low-heat-generating rubber is used for the tread, the braking performance on wet roads (hereinafter also referred to as wet performance) will be reduced. It is difficult to achieve a good balance between rolling resistance and wet performance. Various studies have been conducted with the goal of reducing rolling resistance and improving wet performance (for example, Patent Document 1 below).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-2008 Summary of the Invention

[0006] Technical problem to be solved by the invention

[0007] For environmental reasons, it is necessary to further reduce the rolling resistance of tires.

[0008] Typically, tires installed on vehicles are given a negative camber angle. Consequently, the tire's contact patch length is longer on the inside of the vehicle's width and shorter on the outside. By taking the contact patch shape of the tire installed on the vehicle into account, rolling resistance is expected to be further reduced, leading to improved wet performance.

[0009] The present invention has been made in view of these circumstances, and an object of the present invention is to provide a tire capable of reducing rolling resistance and improving wet performance.

[0010] Technical solutions to technical problems

[0011] The inventors have discovered that, in terms of the performance of grip, an outer tread provided on the outer side of the inner tread contributes more to the performance of grip than an inner tread provided on the inner side of a passenger car (hereinafter referred to as a vehicle), leading to the completion of the present invention. Specifically, a tire according to one embodiment of the present invention includes a tread forming a tread surface. The tread is designated relative to the direction of the vehicle, and of the two ends of the tread, the end arranged on the inner side in the width direction of the vehicle is a first end, and the end arranged on the outer side is a second end, and the tread includes: a base layer; an intermediate layer, which is radially located on the outside of the base layer and covers the base layer; and a crown layer, which is radially located on the outside of the intermediate layer and covers the intermediate layer; the crown layer includes the tread surface, the loss tangent of the intermediate layer at 30°C is lower than the loss tangent of the crown layer at 30°C, the loss tangent of the base layer at 30°C is lower than the loss tangent of the intermediate layer at 30°C, and at least 4 land portions are formed by engraving at least 3 circumferential grooves on the tread. The tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and a load of 50% of the regular load is applied to the tire with the camber angle of the tire set to -1°. The ground contact patch obtained by the tire contacting a flat road surface is referred to as a reference ground contact patch. In the reference ground contact patch, the land portion with the longest ground contact length is referred to as the longest land portion, and the land portion with the shortest ground contact length is referred to as the shortest land portion. The ratio of the thickness of the intermediate layer in the longest land portion to the thickness of the intermediate layer in the shortest land portion is greater than 1.0 and less than or equal to 3.5.

[0012] Preferably, in this tire, the intermediate layer is thicker on the first end side and thinner on the second end side.

[0013] Preferably, in this tire, a contact patch obtained by mounting the tire on a regular rim, adjusting the internal pressure of the tire to 230 kPa, applying a load of 70% of a regular load to the tire with the camber angle of the tire set to 0°, and making the tire contact a flat road surface serves as a reference contact patch. Within the reference contact patch, a ratio of the axial width of the thick region of the intermediate layer to the contact width of the reference contact patch is not less than 40% and not more than 100%.

[0014] Preferably, in this tire, the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and when no load is applied to the tire, in the meridian section of the tire, the contour of the tread surface is composed of a circular arc, which is represented by a plurality of curved contour lines arranged axially in parallel. The curved contour line located in the center of the plurality of curved contour lines is the center curved contour line, and the radius of the center curved contour line is greater than 500 mm and less than 1000 mm.

[0015] Preferably, in the tire, a ratio of a loss tangent of the crown layer at 30° C. to a loss tangent of the intermediate layer at 30° C. is not less than 125% and not more than 200%.

[0016] Effects of the Invention

[0017] According to the present invention, it is possible to obtain a tire having improved wet performance while reducing rolling resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention.

[0019] Figure 2 It is an enlarged cross-sectional view showing the outline of the shoulder portion of the tire.

[0020] Figure 3 This is a schematic diagram illustrating the camber angle of a tire.

[0021] Figure 4 is a schematic diagram illustrating a reference ground plane.

[0022] Figure 5 It is a cross-sectional view showing the outline of the tread surface.

[0023] Figure 6 This is a cross-sectional view showing a portion of a tire of Comparative Example 2.

[0024] Figure 7 This is a cross-sectional view showing a portion of a tire of Comparative Example 3.

[0025] Description of Reference Numerals

[0026] 2…Tires

[0027] 4…Tread

[0028] 6…Sidewall

[0029] 24, 24s, 24m…circumferential groove

[0030] 26, 26s, 26m, 26c…Land Department

[0031] 44…crown layer

[0032] 46…Middle layer

[0033] 48…basal layer DETAILED DESCRIPTION

[0034] Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to appropriate drawings.

[0035] In the present disclosure, a state in which a tire is mounted on a regular rim, the tire internal pressure is adjusted to a regular internal pressure, and the tire is unloaded is referred to as a regular state.

[0036] The tire is mounted on a regular rim, the tire internal pressure is adjusted to 230kPa, and the tire is in an unloaded state. This is called the standard state.

[0037] Unless otherwise specified, dimensions and angles of various tire components are measured in a normal condition. Dimensions and angles that cannot be measured when the tire is mounted on a normal rim are obtained by cutting the tire along a plane containing the axis of rotation. In the cross-section of the tire, the distance between the left and right beads is measured so that it matches the distance between the beads of a tire mounted on a normal rim.

[0038] A regular rim is a rim defined in the standard to which the tire is based. Regular rims are "standard rims" in the JATMA standard, "design rims" in the TRA standard, and "measuring rims" in the ETRTO standard.

[0039] The normal internal pressure refers to the internal pressure defined in the tire's standards. For JATMA standards, this is the "maximum air pressure," for TRA standards, it is the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO standards, it is "INFLATION PRESSURE."

[0040] The normal load refers to the load defined in the tire's standards. For JATMA standards, this is the "maximum load capacity," for TRA standards, it is the "maximum value" specified in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO standards, it is "LOAD CAPACITY."

[0041] In the present disclosure, crosslinked rubber is a molded product of a rubber composition obtained by pressurizing and heating the rubber composition. A rubber composition is a non-crosslinked rubber obtained by mixing a base rubber and chemicals in a mixer such as a Banbury mixer. Crosslinked rubber is also referred to as vulcanized rubber, and a rubber composition is also referred to as unvulcanized rubber.

[0042] Examples of base rubbers include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), nitrile rubber (NBR), and isobutylene-isoprene rubber (IIR). Examples of chemicals include carbon black, reinforcing agents such as silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The choice of base rubber and chemicals, as well as the content of the selected chemicals, are appropriately determined based on the specifications of the tread, sidewall, and other components of the rubber composition.

[0043] In the present disclosure, among the elements constituting the tire, the loss tangent (also referred to as tan δ) of the element formed of crosslinked rubber at a temperature of 30°C is measured under the following conditions using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) in accordance with the provisions of JIS K6394.

[0044] Initial strain = 10%

[0045] Dynamic strain = 2%

[0046] Frequency = 10 Hz

[0047] Deformation Mode = Stretch

[0048] In this measurement, a test piece is sampled from the tire. If it is not possible to sample a test piece from the tire, a sheet of crosslinked rubber (hereinafter also referred to as a rubber sheet) is obtained by pressurizing and heating the rubber composition used in the element to be measured at 170°C for 12 minutes.

[0049] Figure 1 1 is a part of a tire according to an embodiment of the present invention. The tire 2 is a tire for a passenger car. Figure 1 ] shows a portion of a cross section (hereinafter also referred to as a meridian cross section) of the tire 2 along a plane including the rotation axis of the tire 2. Figure 1 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 1 The direction of the paper surface is the circumferential direction of the tire 2 .

[0050] exist Figure 1 In FIG, the alternate long and short dashed line CL is the equatorial plane of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane CL, except for the tread pattern, patterns, characters and other decorations engraved on its outer surface and the internal structure of the tread described below.

[0051] The tire 2 is mounted on a rim R. The rim R is a standard rim. The tire 2 is filled with air, and its internal pressure can be adjusted. The tire 2 mounted on the rim R is also referred to as a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on the rim R.

[0052] exist Figure 1 In FIG, the position indicated by symbol PW is the axial outer end of the tire 2. When the outer surface is decorated with patterns, characters, etc., the outer end PW is determined based on an imaginary outer surface obtained by assuming that there is no decoration.

[0053] exist Figure 1 In the diagram, the length denoted by WA is the maximum width of the tire 2, or the cross-sectional width (see JATMA, etc.). The cross-sectional width WA of the tire 2 is the axial distance from one outer end PW to the other outer end PW. The outer end PW is the location where the tire 2 has its maximum width (hereinafter referred to as the maximum width location). The cross-sectional width WA is measured on the tire 2 in a standard state.

[0054] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinchers 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a carcass ply 16 , a pair of scuff layers 18 , and an inner liner 20 .

[0055] The tread 4 forms a tread surface T. The tire 2 comes into contact with the road surface at the tread surface T. Grooves 22 are engraved on the tread 4. These constitute a tread pattern.

[0056] The grooves 22 constituting the tread pattern include circumferential grooves 24 extending continuously in the circumferential direction. In the tire 2, at least three circumferential grooves 24 are engraved on the tread 4. Thus, at least four land portions 26 are formed on the tread 4. Figure 1 In the tire 2 shown in FIG, five land portions 26 are formed by engraving four circumferential grooves 24 in the tread 4 .

[0057] The tread 4 of the tire 2 has a tread body 28 and a pair of wings 30. Each wing 30 is located axially outside the tread body 28. The wings 30 connect the tread body 28 and the sidewall 6. Considering adhesion, the wings 30 are made of cross-linked rubber.

[0058] exist Figure 1 In the figure, the position indicated by the symbol TE is the end of the tread 4. In the tire 2, the direction of the tread 4 is specified relative to the vehicle. Figure 1 The end TE of the tread 4 on the right side of the drawing is the first end TE1, and the end TE of the tread 4 on the left side is the second end TE2. When the tire 2 is mounted on a vehicle, of the two ends of the tread 4, the first end TE1 of the tread 4 is located inward in the vehicle width direction. The second end TE2 of the tread 4 is located outward in the vehicle width direction.

[0059] exist Figure 1 , the position indicated by symbol PE is the equator of the tire 2. The equator PE is the intersection of the tread surface T and the equatorial plane CL. When grooves 22 are provided on the equatorial plane CL, the equator PE is determined based on an imaginary tread surface obtained by assuming that there are no grooves 22 on the equatorial plane CL.

[0060] In the tread 4 of the tire 2 , the portion from the equator PE to the first end TE1 is also referred to as the inner tread 4a , and the portion from the equator PE to the second end TE2 is also referred to as the outer tread 4b .

[0061] exist Figure 1 , the position indicated by symbol PH is a position on the tread surface T. The position PH corresponds to the axially outer end of the contact patch of the tire 2 with the road surface.

[0062] The contact patch used to determine the position PH can be obtained, for example, by a contact patch shape measuring device (not shown). The contact patch is obtained by applying a load of 70% of the normal load to the tire 2 as a longitudinal load in a state where the camber angle of the tire 2 is 0° in a standard state in the device, and making the tire 2 contact a flat road surface. In the tire 2, the contact patch thus obtained is the reference contact patch, and the position on the tread surface T corresponding to the axial outer end of the reference contact patch is the above-mentioned position PH. In the tire 2, the position PH is the reference ground contact end. Figure 1 In the diagram, the length indicated by symbol WH is the ground contact width of the reference ground contact patch. Ground contact width WH is the axial distance from one reference ground contact end PH to the other reference ground contact end PH. Ground contact width WH is measured when the tire 2 is in a standard state.

[0063] Each sidewall 6 is connected to the end TE of the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the end TE of the tread 4 along the carcass 12 toward the clinch 8. The sidewall 6 is made of cross-linked rubber in consideration of cut resistance.

[0064] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 contacts the rim R. The clinch 8 is made of a cross-linked rubber in consideration of wear resistance.

[0065] Each bead 10 is located axially inside the clinch portion 8. The bead 10 has a core 32 and an apex 34. Although not shown, the core 32 includes a steel wire.

[0066] The apex 34 is located radially outside the core 32. The apex 34 tapers outwardly. The apex 34 is made of a highly rigid cross-linked rubber.

[0067] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinch portions 8. The carcass 12 is spanned between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0068] The carcass 12 includes at least one carcass ply 36. The carcass 12 of the tire 2 is composed of two carcass plies 36. The carcass ply 36 located radially inward of the tread 4 is a first carcass ply 38, and the carcass ply 36 located outward of the first carcass ply 38 is a second carcass ply 40. From the perspective of weight reduction, the carcass 12 can also be composed of a single carcass ply 36.

[0069] The first carcass ply 38 includes a first ply body 38 a spanning between one core 32 and the other core 32 and a pair of first turn-back portions 38 b connecting the first ply body 38 a and turned back around each core 32 from the axial inside toward the outside.

[0070] The second carcass ply 40 includes a second ply body 40 a spanning between one core 32 and the other core 32 and a pair of second turn-back portions 40 b connecting the second ply body 40 a and turned back around each core 32 from the axial inside toward the outside.

[0071] Although not shown, the carcass ply 36 includes a plurality of carcass cords arranged in parallel. Each carcass cord intersects the equatorial plane CL. The carcass cords are cords made of organic fibers, such as nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0072] The belt layer 14 is located radially inside the tread 4. The belt layer 14 is radially superimposed on the carcass 12 from the outside. Figure 1 In FIG. 1 , the length indicated by symbol WR is the axial width of the belt layer 14. The axial width WR is the axial distance from one end to the other end of the belt layer 14. In the tire 2, the axial width WR of the belt layer 14 is not less than 65% and not more than 85% of the cross-sectional width WA.

[0073] The belt layer 14 is composed of at least two layers 42 laminated in the radial direction. The belt layer 14 of the tire 2 is composed of two layers 42 laminated in the radial direction. Of the two layers 42, the layer 42 located on the inner side is the inner layer 42a, and the layer 42 located on the outer side is the outer layer 42b. Figure 1 As shown, the inner layer 42a is wider than the outer layer 42b. The length from the end of the outer layer 42b to the end of the inner layer 42a is 3 mm to 10 mm.

[0074] Although not shown, each of the inner layer 42a and the outer layer 42b includes a plurality of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane CL. The material of the belt cord is steel.

[0075] The carcass layer 16 is radially located between the tread 4 and the belt layer 14. The carcass layer 16 is stacked on the belt layer 14 on the inner side of the tread 4. The carcass layer 16 has a seamless structure.

[0076] Although not shown, the carcass ply 16 includes helically wound carcass cords. The carcass cords extend substantially in the circumferential direction. Specifically, the carcass cords form an angle of 5° or less with respect to the circumferential direction. The tire 2 utilizes carcass cords made of organic fibers, such as nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0077] The tire ply 16 of the tire 2 is formed of full plies with opposite ends across the equator PE. The ply 16 is wider than the belt 14. The length from the end of the belt 14 to the end of the ply 16 is 3 mm to 7 mm. The ply 16 radially covers the belt 14 from the outside. The ply 16 may also include a pair of edge plies spaced axially to cover the ends of the full ply and the ends of the belt 14. Alternatively, the ply 16 may consist solely of a pair of edge plies.

[0078] Each anti-scuff layer 18 is located radially inward of the bead 10. The anti-scuff layer 18 is in contact with the rim R. The anti-scuff layer 18 of the tire 2 is made of cloth and rubber impregnated with the cloth.

[0079] The inner liner 20 is located inside the carcass 12. The inner liner 20 forms the inner surface of the tire 2. The inner liner 20 is made of a cross-linked rubber with a low gas permeability coefficient. The inner liner 20 maintains the internal pressure of the tire 2.

[0080] Figure 2 express Figure 1 A portion of a tire 2 is shown in FIG. Figure 2 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 2 The direction of the paper surface is the circumferential direction of the tire 2 .

[0081] exist Figure 2 , the outline of the shoulder portion of the tire 2 is shown in a meridian cross section. Figure 2 The profile shown in FIG is obtained by measuring the outer surface shape of the tire 2 in a standard state by a displacement sensor. Figure 2 1 shows the profile of the outer surface of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0082] For example, the tread 4 has grooves 22 engraved therein. The sidewall 6 is provided with decorative patterns, text, and other decorations. Therefore, the outer surface shape of the tire 2 obtained through measurement includes concave and convex portions corresponding to the grooves 22, patterns, text, and other decorations. The outer surface profile of the tire 2 is a hypothetical outer surface obtained by assuming that these concave and convex portions do not exist.

[0083] In a meridian cross-section, the profile of the outer surface of the tire 2 (hereinafter referred to as the tire outer surface TS) is formed by connecting a plurality of contour lines formed by straight lines or circular arcs. In this disclosure, contour lines formed by straight lines or circular arcs are simply referred to as contour lines. Contour lines formed by straight lines are referred to as linear contour lines, and contour lines formed by circular arcs are referred to as curved contour lines.

[0084] The tire outer surface TS has a tread surface T and a pair of side surfaces S connected to the end portions of the tread surface T. In a meridian cross-section, the profile of the tread surface T includes a plurality of curved contour lines having different radii. In this tire 2, among the plurality of curved contour lines included in the profile of the tread surface T, the curved contour line having the smallest radius is located at the end portion of the tread surface T and is connected to the side surfaces S. In a meridian cross-section, the profile of the tire outer surface TS is formed by the arc having the smallest radius among the plurality of curved contour lines included in the profile of the tread surface T, and the curved portion of the curved contour line connected to the side surfaces S is included at the end portion of the tread surface T. Figure 2 In FIG, the curved portion is represented by the symbol RS.

[0085] In the profile of the tire's outer surface TS, the curved portion RS is tangent to a contour line axially adjacent to the inner side of the curved portion RS (hereinafter referred to as an inner adjacent contour line NT) at a contact point CT. The curved portion RS is tangent to a contour line forming the profile of the side surface S axially adjacent to the outer side of the curved portion RS (hereinafter referred to as an outer adjacent contour line NS) at a contact point CS. The profile of the tire's outer surface TS includes an inner adjacent contour line NT located axially inward of the curved portion RS and tangent to the curved portion RS, and an outer adjacent contour line NS located axially outward of the curved portion RS and tangent to the curved portion RS.

[0086] exist Figure 2 In the figure, solid line LT is a tangent to the curved portion RS at the contact point CT between the inner adjacent contour line NT and the curved portion RS. Solid line LS is a tangent to the curved portion RS at the contact point CS between the outer adjacent contour line NS and the curved portion RS. The position denoted by symbol PT is the intersection of contact lines LT and LS. In this tire 2, this intersection point PT is the tread reference end.

[0087] exist Figure 1 In the figure, the length indicated by the two arrows WT is the tread width. This tread width WT is the axial distance from one tread reference end PT to the other tread reference end PT. In this tire 2, the ratio of the tread width WT to the cross-section width WA (WT / WA) is 70% or more and 90% or less. The ratio of the ground contact width WH of the reference contact patch to the tread width WT (WH / WT) is 70% or more and 90% or less.

[0088] As described above, the tread 4 of the tire 2 has four circumferential grooves 24. In the tire 2, there are no particular restrictions on the arrangement, groove depth, and groove width of the four circumferential grooves 24. Typical arrangements, groove depths, and groove widths can be applied to the tread 4 as the arrangement, groove depth, and groove width of the circumferential grooves of a tire.

[0089] In this tire 2, the circumferential groove 24 located axially outward among the four circumferential grooves 24 is the shoulder circumferential groove 24s, and the circumferential groove 24 located inside the shoulder circumferential groove 24s is the middle circumferential groove 24m.

[0090] As described above, the tread 4 of the tire 2 is formed with five land portions 26. Of the five land portions 26, the land portion 26 located axially outward is the shoulder land portion 26s. The land portion 26 located axially inward of the shoulder land portion 26s is the middle land portion 26m. The land portion 26 located between the left and right middle land portions 26m is the center land portion 26c. This center land portion 26c is located on the equatorial plane CL.

[0091] In this tire 2, the shoulder land portion 26s on the first end TE1 side of the tread 4 is a first shoulder land portion 26s1, and the shoulder land portion 26s on the second end TE2 side is a second shoulder land portion 26s2. The middle land portion 26m on the first end TE1 side of the tread 4 is a first middle land portion 26m1, and the middle land portion 26m on the second end TE2 side is a second middle land portion 26m2.

[0092] Figure 3 The figure shows a state of the tire 2 mounted on a vehicle (not shown). Figure 3 The right side of the paper is the inner side in the width direction of the vehicle, and the left side is the outer side in the width direction of the vehicle.

[0093] like Figure 3 As shown, the tire 2 is usually mounted on the vehicle with the equatorial plane CL tilted relative to the road surface. Figure 3 In the diagram, the solid line denoted by the symbol BL is a straight line perpendicular to the flat road surface in contact with the tire 2. When the road surface is horizontal, this straight line BL is also called a vertical line. Angle θ is the angle formed by the equatorial plane CL with respect to this straight line BL. This angle θ is also called the camber angle. Figure 3 The tire 2 shown in FIG is mounted on the vehicle so that the upper portion of the equatorial plane CL is located further inward than the lower portion thereof in the width direction of the vehicle. The camber angle of the tire 2 thus mounted is also called a negative camber angle and is represented by a negative angle. Figure 3 The tire 2 shown in FIG. 1 is in a state of having a negative camber angle.

[0094] exist Figure 4 An image of the contact patch of the tire 2 is shown in FIG. Figure 4In FIG, the up-down direction corresponds to the circumferential direction of the tire 2, and the left-right direction corresponds to the axial direction of the tire 2. Figure 4 The right side of the paper is the inner side in the width direction of the vehicle, in other words, the first end TE1 side of the tread 4. The left side of the paper is the outer side in the width direction of the vehicle, in other words, the second end TE2 side of the tread 4.

[0095] This contact patch is obtained using, for example, the aforementioned contact patch shape measuring device (not shown). In this device, the contact patch is obtained by setting the camber angle θ of the tire 2 in a normal state to -1°, applying a longitudinal load of 50% of the normal load to the tire 2, and causing the tire 2 to contact a flat road surface. In this disclosure, this contact patch is referred to as the reference contact patch.

[0096] Tires mounted on vehicles (particularly, passenger cars) generally have a negative camber angle. The reference ground contact surface is a ground contact surface that takes into account the ground contact state of the tire mounted on the vehicle.

[0097] As described above, five land portions 26 are formed on the tread 4 of the tire 2. The reference ground contact surface includes the ground contact surface CA corresponding to the five land portions 26. Figure 4 , the contact patch CA1 of the first shoulder land portion 26s1, the contact patch CA2 of the first middle land portion 26m1, the contact patch CA3 of the center land portion 26c, the contact patch CA4 of the second middle land portion 26m2, and the contact patch CA5 of the second shoulder land portion 26s2 are shown in order from the right side of the paper.

[0098] In this Figure 4 In the diagram, the length LM1 represents the ground contact length of the first middle land portion 26m1 at the ground contact surface CA2, and the length LS2 represents the ground contact length of the second shoulder land portion 26s2 at the ground contact surface CA5.

[0099] In this tire 2, of the five land portions 26 included in the reference ground contact patch, the first middle land portion 26m1 has the longest ground contact length in its ground contact patch CA2. The second shoulder land portion 26s2 has the shortest ground contact length in its ground contact patch CA5. In the present disclosure, among the land portions 26 included in the reference ground contact patch, the land portion 26 with the longest ground contact length is the longest land portion 26w, and the land portion 26 with the shortest ground contact length is the shortest land portion 26n. In this tire 2, the first middle land portion 26m1 is the longest land portion 26w, and the second shoulder land portion 26s2 is the shortest land portion 26n.

[0100] like Figure 1 As shown, the tread 4 of the tire 2 (specifically, the tread body 28 ) includes a base layer 44 , an intermediate layer 46 , and a cap layer 48 .

[0101] The base layer 44 is located radially inward of the intermediate layer 46 and the crown layer 48. The base layer 44 is located radially outward of the carcass layer 16. The base layer 44 is stacked on the carcass layer 16. The base layer 44 covers the carcass layer 16 from the outside in the radial direction.

[0102] The intermediate layer 46 is radially located between the base layer 44 and the crown layer 48. The intermediate layer 46 is radially located outside the base layer 44. The intermediate layer 46 is stacked on the base layer 44. The intermediate layer 46 covers the base layer 44 from the outside in the radial direction.

[0103] The crown layer 48 is located radially outward from the base layer 44 and the middle layer 46. The crown layer 48 includes a tread surface T. The crown layer 48 is located radially outward from the middle layer 46. The crown layer 48 is stacked on the middle layer 46. The crown layer 48 covers the middle layer 46 from the outside in the radial direction.

[0104] The base layer 44, the middle layer 46, and the crown layer 48 are each made of a cross-linked rubber having different heat generation properties. In this tire 2, the loss tangent LTm of the middle layer 46 at 30°C is lower than the loss tangent LTc of the crown layer 48 at 30°C. The loss tangent LTb of the base layer 44 at 30°C is lower than the loss tangent LTm of the middle layer 46 at 30°C.

[0105] In this tire 2, the crown layer 48 is most susceptible to heat generation and contributes to the tire 2's ability to exert grip. The base layer 44 is least susceptible to heat generation and contributes to reducing the tire 2's rolling resistance. The middle layer 46 is less susceptible to heat generation than the crown layer 48 and more susceptible to heat generation than the base layer 44. The middle layer 46 contributes to reducing rolling resistance more than the crown layer 48 and contributes to the exertion of grip more than the base layer 44.

[0106] Each land portion 26 formed in the tread 4 is composed of three layers: a base layer 44, an intermediate layer 46, and a crown layer 48. Figure 4 As shown, the ground contact length of the reference ground contact surface land portion 26 varies depending on the position. As described above, the reference ground contact surface is a ground contact surface that takes into account the ground contact state of the tire mounted on the vehicle.

[0107] The inventors took into consideration the ground contact shape of tires mounted on vehicles and conducted in-depth research on the treads. They discovered that, in terms of the performance of grip, the outer treads arranged on the outer side of a passenger car (hereinafter also referred to as vehicles) contribute more than the inner treads arranged on the inner side. In order to ensure wet performance while reducing rolling resistance, they focused on the thickness of the middle layer of the land portion, and considered using mainly heat-generating rubber for the outer tread and mainly low-heat-generating rubber for the inner tread, thereby completing the present invention.

[0108] In the present disclosure, the thickness of the intermediate layer 46 of the shoulder land portion 26s is the thickness of the intermediate layer 46 measured along the normal line of the interface between the intermediate layer 46 and the base layer 44, using the boundary between the shoulder land portion 26s and the shoulder circumferential groove 24s on the tread surface T, that is, the position on the tread surface T 5 mm away from the edge of the shoulder land portion 26s as the reference position. Figure 1 In FIG. 4 , the straight line denoted by symbol SN is a normal line passing through the interface between the intermediate layer 46 and the base layer 44 at a position 5 mm from the edge of the second shoulder land portion 26s2. The thickness of the intermediate layer 46 in the second shoulder land portion 26s2 is measured along the normal line SN.

[0109] In the present disclosure, the thickness of the intermediate layer 46 in the land portion 26 other than the shoulder land portion 26s is measured by taking the width center of the land portion 26 on the tread surface T as a reference position and passing through the normal line along the interface between the intermediate layer 46 and the base layer 44 at this reference position, and is expressed as the thickness of the intermediate layer 46. Figure 1 In the figure, the straight line indicated by symbol LN is the normal line passing through the width center of the first middle land portion 26m1 and the interface between the middle layer 46 and the base layer 44. In the first middle land portion 26m1, the thickness of the middle layer 46 is measured along the normal line LN.

[0110] As described above, in this tire 2 , the first middle land portion 26m1 is the longest land portion 26w, and the second shoulder land portion 26s2 is the shortest land portion 26n.

[0111] exist Figure 1 TL is the thickness of the intermediate layer 46 in the first middle land portion 26m1, which is the longest land portion 26w. TS is the thickness of the intermediate layer 46 in the second shoulder land portion 26s2, which is the shortest land portion 26n.

[0112] In the present disclosure, when the thickness of the intermediate layer 46 in the longest land portion 26w varies, the thickness TL of the intermediate layer 46 in the longest land portion 26w is represented by the maximum thickness, not the thickness at the reference position described above. When the thickness of the intermediate layer 46 in the shortest land portion 26n varies, the thickness TS of the intermediate layer 46 in the shortest land portion 26n is represented by the minimum thickness, not the thickness at the reference position described above. When the shoulder land portion 26s is the shortest land portion 26n, the minimum thickness is determined at the portion that radially overlaps the reference ground contact patch.

[0113] In this tire 2, the crown layer 48, which has excellent wear resistance, radially covers the entire intermediate layer 46 from the outside. Since the intermediate layer 46, which has disadvantages in terms of wear resistance, is not exposed to the tread surface T, abnormal wear of the tread 4 can be prevented. In this tire 2, uneven wear is less likely to occur.

[0114] In this tire 2, when mounted on a vehicle, a longest land portion 26w is formed on the inner tread 4a, which is positioned inwardly, and a shortest land portion 26n is formed on the outer tread 4b, which is positioned outwardly. Furthermore, the ratio (TL / TS) of the thickness TL of the intermediate layer 46 in the longest land portion 26w to the thickness TS of the intermediate layer 46 in the shortest land portion 26n is greater than 1.0 and less than or equal to 3.5.

[0115] In this tire 2, the middle layer 46, which contributes more to the rolling resistance than the crown layer 48, is thicker in the longest land portion 26w. This tread 4 contributes to effectively reducing the rolling resistance.

[0116] Because the intermediate layer 46 in the shortest land portion 26n is thin, this tire 2 can form a thicker crown layer 48 on the outer tread 4b, which contributes to grip. Since the crown layer 48 contributes more to grip than the intermediate layer 46, this tread 4 can contribute to improved grip. Since the ratio (TL / TS) is less than 3.5, the crown layer 48 is formed with an appropriate thickness on the inner tread 4a, and the intermediate layer 46 is formed with an appropriate thickness on the outer tread 4b.

[0117] The tire 2 can reduce rolling resistance while improving wet performance.

[0118] As described above, in this tire 2, the ratio (TL / TS) is greater than 1.0 and less than or equal to 3.5. To effectively reduce rolling resistance and improve wet performance, this ratio (TL / TS) is preferably 1.1 or greater, more preferably 1.2 or greater, even more preferably 1.3 or greater, and particularly preferably 1.4 or greater. From the same perspective, this ratio (TL / TS) is preferably 3.3 or less, more preferably 3.1 or less, even more preferably 2.9 or less, and particularly preferably 2.7 or less.

[0119] like Figure 1 As shown, in this tire 2 , the intermediate layer 46 is thicker on the first end TE1 side of the tread 4 and thinner on the second end TE2 side.

[0120] In this tire 2, the inner tread 4a helps effectively reduce rolling resistance, while the outer tread 4b helps effectively exert grip. This tire 2 can achieve both reduced rolling resistance and improved wet performance. From this perspective, the intermediate layer 46 is preferably thicker on the first end TE1 side of the tread 4 and thinner on the second end TE2 side. In this tire 2, the intermediate layer 46 is preferably thicker than the crown layer 48 on the first end TE1 side of the tread 4 and thinner than the crown layer 48 on the second end TE2 side.

[0121] As described above, the intermediate layer 46 of the tire 2 is thicker on the first end TE1 side of the tread 4 and thinner on the second end TE2 side.

[0122] From the perspective of being able to form an intermediate layer 46 that helps to effectively reduce rolling resistance and improve grip, on the first end TE1 side, the thickness of the intermediate layer 46 is preferably set to be greater than 50% of the ratio of the total thickness of the intermediate layer 46 and the crown layer 48, and on the second end TE2 side, the thickness of the intermediate layer 46 is preferably set to be less than 50% of the ratio of the total thickness of the intermediate layer 46 and the crown layer 48.

[0123] exist Figure 1 In the figure, the position denoted by symbol PB indicates the position where the ratio of the thickness of the intermediate layer 46 to the total thickness of the intermediate layer 46 and the crown layer 48 is 50%. In this tire 2, this position PB is the boundary between the thick region of the intermediate layer 46 on the first end TE1 side and the thin region of the intermediate layer 46 on the second end TE2 side. In this tire 2, the boundary PB is preferably formed between the longest land portion 26w and the shortest land portion 26n described above.

[0124] In this Figure 1 The length indicated by symbol WM is the axial width of the thick region of the intermediate layer 46 formed on the first end TE1 side. This axial width is represented by the axial distance from the boundary PB to the reference ground terminal PH on the first end TE1 side (hereinafter referred to as the first reference ground terminal PH1).

[0125] In the tire 2 , in the reference contact patch, the ratio (WM / WH) of the axial width WM of the thick region of the intermediate layer 46 to the contact patch width WH of the reference contact patch is preferably 40% to 100%.

[0126] By setting the ratio (WM / WH) to 40% or more, the inner tread 4a can effectively contribute to reducing rolling resistance. From this perspective, the ratio (WM / WH) is preferably 50% or more, more preferably 60% or more.

[0127] By setting the ratio (WM / WH) to 100% or less, the outer tread 4b can contribute to ensuring grip. From this perspective, the ratio (WM / WH) is preferably 85% or less, more preferably 75% or less.

[0128] exist Figure 1 , the length denoted by symbol AL is the total thickness of the crown layer 48 and the intermediate layer 46 in the longest land portion 26w. This total thickness AL is measured along the normal line LN.

[0129] In this tire 2, from the perspective of effectively contributing to the reduction of rolling resistance in longest land portion 26w, the ratio (TL / AL) of the thickness TL of intermediate layer 46 in longest land portion 26w to the total thickness AL of crown layer 48 and intermediate layer 46 is preferably 50% or greater, more preferably 60%. From the perspective of forming a crown layer 48 having an appropriate thickness in longest land portion 26w, the ratio (TL / AL) is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less.

[0130] exist Figure 1 , the length indicated by symbol AS is the total thickness of the crown layer 48 and the intermediate layer 46 in the shortest land portion 26n. The total thickness AS is measured along the normal line SN.

[0131] In this tire 2, from the perspective of effectively contributing to improved grip in the shortest land portion 26n, the ratio (TS / AS) of the thickness TS of the intermediate layer 46 in the shortest land portion 26n to the total thickness AS of the crown layer 48 and the intermediate layer 46 is preferably 50% or less, and more preferably 40% or less. From the perspective of forming the intermediate layer 46 having an appropriate thickness in the shortest land portion 26n, the ratio (TS / AS) is preferably 20% or more, and more preferably 25% or more.

[0132] Figure 5 Indicates Figure 1 A portion of a tire 2 is shown in FIG. Figure 5 In FIG, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. Figure 5 The vertical direction of the paper is the circumferential direction of the tire 2.

[0133] exist Figure 5 , the profile of the tread surface T of the tire 2 in a meridian cross section is shown. Figure 5 The outline shown in Figure 2 The profiles shown in FIG are similar and are obtained by measuring the outer surface shape of the tire 2 in the standard state by a displacement sensor. Figure 5 , there is shown the profile of the tread surface T of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0134] The tread surface T of the tire 2 is divided into a plurality of axially parallel regions in a meridian cross-section. These regions include a crown region Cr, a pair of intermediate regions Mi, and a pair of lateral regions Sd. The crown region Cr is located axially at the center. The crown region Cr includes the equator PE. Each intermediate region Mi is axially outward of the crown region Cr. Each lateral region Sd is axially outward of the intermediate region Mi.

[0135] exist Figure 5 In the diagram, the position denoted by symbol CM is the boundary between the crown region Cr and the middle region Mi. The position denoted by symbol MS is the boundary between the middle region Mi and the side region Sd. Symbol SE is the outer end of the side region Sd. The outer end SE is also the contact point CT described above.

[0136] As described above, the profile of the tread surface T includes a plurality of curved contour lines having different radii. The profile of each region is represented by a curved contour line. In this tire 2, the curved contour line representing the profile of the crown region Cr is also referred to as the center contour line. The curved contour line representing the profile of the middle region Mi is also referred to as the middle contour line. The curved contour line representing the profile of the side region Sd is also referred to as the side contour line. The plurality of curved contour lines included in the profile of the tread surface T include a center contour line, a pair of middle contour lines, and a pair of side contour lines. The center contour line is the curved contour line located at the center of the plurality of curved contour lines representing the profile of the tread surface T.

[0137] Although not shown, the center of the central contour line is located on the equatorial plane CL. Figure 5 In the figure, the one-way arrow represented by symbol Rc is the radius of the center contour line. The intermediate contour line is tangent to the center contour line at the boundary CM. Figure 5 In the figure, the one-way arrow represented by symbol Rm is the radius of the middle contour line. The side contour line is tangent to the middle contour line at the boundary MS. Figure 5 In the figure, the one-way arrow represented by the symbol Rd is the radius of the side profile line.

[0138] In this tire 2, the centerline radius Rc is preferably 500 mm to 1000 mm. This allows the tread 4 to fully demonstrate its performance. In this tire 2, the longest land portion 26w is formed axially outward at a position 40% of the ground contact width WH of the ground contact patch from the first reference ground contact edge PH1, and the shortest land portion 26n is formed axially outward at a position 75% of the ground contact width WH of the ground contact patch from the first reference ground contact edge PH1. This tire 2 can achieve both reduced rolling resistance and improved wet performance. To this end, the centerline radius Rc is more preferably 600 mm or greater, and even more preferably 700 mm or greater. It is more preferably 900 mm or less, and even more preferably 800 mm or less.

[0139] In the present disclosure, the radius Rc of the central contour line is defined as the radius of an arc having a center on the equatorial plane CL and passing through the left and right edges of the central land portion 26 c and the equator PE. In a tread having circumferential grooves engraved on the equatorial plane CL, the radius Rc of the central contour line is defined as the radius of an arc having a center on the equatorial plane CL and passing through the edges of the land portions located on both sides of the circumferential grooves.

[0140] In this tire 2, the radius Rm of the middle contour line is smaller than the radius Rc of the center contour line, and the radius Rd of the side contour line is smaller than the radius Rm of the middle contour line. As a result, each contour line is smoothly connected, forming a tread 4 that can fully exert its function. In this tire 2, cornering stability and straight-line driving stability are balanced. From this perspective, the ratio of the radius Rm of the middle contour line to the radius Rc of the center contour line (Rm / Rc) is preferably greater than 0.50 and less than 0.54. The ratio of the radius Rd of the side contour line to the radius Rc of the center contour line (Rd / Rc) is preferably greater than 0.20 and less than 0.24.

[0141] In this tire 2, the loss tangent LTc of the crown layer 48 at 30°C is higher than the loss tangent LTm of the intermediate layer 46 at 30°C. The crown layer 48 easily heats up, while the intermediate layer 46 does not easily heat up. In this tire 2, the ratio of the loss tangent LTc of the crown layer 48 at 30°C to the loss tangent LTm of the intermediate layer 46 at 30°C (LTc / LTm) is preferably 125% or more and 200% or less.

[0142] By setting the ratio (LTc / LTm) to 125% or more, the crown layer 48 contributes to effective grip, while the middle layer 46 contributes to effective reduction of rolling resistance. From this perspective, the ratio (LTc / LTm) is preferably 140% or more, and more preferably 155% or more.

[0143] By setting the ratio (LTc / LTm) to 200% or less, the impact of the crown layer 48 on rolling resistance can be minimized. By maintaining an appropriate difference in the heat generation between the crown layer 48 and the intermediate layer 46, damage caused by this difference in heat generation is prevented. From this perspective, the ratio (LTc / LTm) is preferably 185% or less, and more preferably 175% or less.

[0144] In this tire 2, the loss tangent LTb of the base layer 44 at 30°C is preferably 0.11 or less. This is because the base layer 44 effectively reduces rolling resistance. From this perspective, the loss tangent LTb is preferably 0.10 or less, and more preferably 0.09 or less. In this tire 2, since the loss tangent LTb of the base layer 44 is preferably as low as possible, no lower limit is set.

[0145] The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.15 or less. This is because the intermediate layer 46 effectively reduces rolling resistance. From this perspective, the loss tangent Ltm is preferably 0.14 or less, and more preferably 0.13 or less. The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.11 or greater. The intermediate layer 46 ensures the necessary rigidity and effectively contributes to improved wet performance. From this perspective, the loss tangent Ltm is more preferably 0.12 or greater.

[0146] The loss tangent LTc of the crown layer 48 at 30°C is preferably not less than 0.15. The crown layer 48 can help improve wet performance. From this perspective, the loss tangent LTc is preferably not less than 0.16, and more preferably not less than 0.17. The crown layer 48 contacts the road surface. From the perspective of improving wet performance, the loss tangent LTc is preferably as high as possible. However, a high loss tangent LTc will cause heat generation. There is a concern that the heated crown layer 48 will cause the temperature of the intermediate layer 46 to exceed expectations. From the perspective of being able to stably maintain the overall temperature state of the tread 4 and maintain low rolling resistance, the loss tangent LTc of the crown layer 48 at 30°C is preferably not more than 0.30, more preferably not more than 0.28, and further preferably not more than 0.27.

[0147] As described above, the present invention provides a tire capable of achieving improved wet performance while reducing rolling resistance.

[0148] [Example]

[0149] Hereinafter, the present invention will be described in more detail with reference to Examples etc. However, the present invention is not limited to the Examples.

[0150] Example 1

[0151] Be prepared Figure 1The basic structure shown in FIG and the pneumatic tire for passenger cars (tire size = 225 / 55R19) with the specifications shown in Table 1 below are provided.

[0152] The radius Rc of the center curve contour line constituting the profile of the tread surface is 750 mm.

[0153] In the reference ground contact surface, the ratio (WM / WH) of the axial width WM of the thick region of the intermediate layer to the ground contact width WH of the reference ground contact surface is 68%.

[0154] In this Example 1, the total thickness AL in the longest land portion and the total thickness AS in the shortest land portion are the same, and the ratio of the thickness TL of the intermediate layer in the longest land portion to the thickness TS of the intermediate layer in the shortest land portion (TL / TS) is 1.50.

[0155] The crown layer had a loss tangent LTc of 0.24 at 30°C. The middle layer had a loss tangent LTm of 0.15 at 30°C. The ratio of loss tangent LTc to loss tangent LTm (LTc / LTm) was 160%. The base layer had a loss tangent LTb of 0.10 at 30°C.

[0156] Comparative Example 1

[0157] Comparative Example 1 is a conventional tire with a tread composed of two layers: a cap layer and a base layer. In Comparative Example 1, the radius Rc of the centerline is set to 450 mm. The base layer has the same structure as that of Example 1.

[0158] In Comparative Example 1, the loss tangent LTc of the crown layer at 30° C. was 0.22.

[0159] The configuration other than the tread is the same as that of the first embodiment.

[0160] Example 2

[0161] The radius Rc of the center curve contour line was set as shown in Table 2 below, and the rest was the same as in Example 1 to obtain a tire of Example 2.

[0162] In this second embodiment, similar to the first embodiment, the first middle land portion is the longest land portion, and the second shoulder land portion is the shortest land portion.

[0163] Comparative Example 2

[0164] Used Figure 6 A tread having the structure shown, and otherwise identical to Example 2, was used to obtain a tire of Comparative Example 2. The tread of Comparative Example 2 includes a crown layer C, an intermediate layer M, and a base layer B. The materials of the crown layer C, intermediate layer M, and base layer B are identical to those of the crown layer, intermediate layer, and base layer of Example 1.

[0165] In this comparative example 2, the middle layer M is laminated on the base layer B on the first end TE1 side, and the crown layer C is laminated on the base layer B on the second end TE2 side.

[0166] The ratio (Wa / WH) of the axial distance Wa from the reference ground contact edge PH on the first end TE1 side to the boundary between the crown layer and the intermediate layer to the ground contact width WH of the reference ground contact surface is 68%. The ratio (Wa / WH) is shown in the "WM / WH" column in Table 1 below.

[0167] Comparative Example 3

[0168] Used Figure 7 The tread of the structure shown and other aspects were the same as those of Example 2, and a tire of Comparative Example 3 was obtained.

[0169] In Comparative Example 3, the middle layer M is laminated on the base layer B. The tread is composed of two layers, the middle layer M and the base layer B, on the first end TE1 side, and three layers, the cap layer C, the middle layer M, and the base layer B, on the second end TE2 side.

[0170] The ratio (Wa / WH) of the axial distance Wa from the reference ground contact edge PH on the first end TE1 side to the boundary between the crown layer and the intermediate layer to the reference ground contact width WH is 68%. The ratio (Wa / WH) is shown in the "WM / WH" column in Table 1 below.

[0171] In Comparative Example 3, similar to Example 2, the first middle land portion is the longest land portion, and the second shoulder land portion is the shortest land portion. The ratio of the thickness of the intermediate layer in the shortest land portion to the total thickness of the crown layer and the intermediate layer is the same as in Example 2.

[0172] Example 3

[0173] The ratio (WM / WH) was set as shown in Table 2 below, and the other conditions were the same as in Example 1, to obtain a tire of Example 3.

[0174] Example 4-5

[0175] The thickness TL and the thickness TS were changed to set the ratio (TL / TS) as shown in Table 2 below. Other conditions were the same as those in Example 1, and tires of Examples 4-5 were obtained.

[0176] Rolling resistance coefficient (RRC)

[0177] The rolling resistance coefficient (RRC) of the trial tires was measured using a rolling resistance tester while running on a drum at 80 km / h under the following conditions. The results are shown in Tables 1 and 2 below as indices with Comparative Example 1 being 100. The larger the value, the lower the rolling resistance of the tire.

[0178] Rim: 19×7J

[0179] Internal pressure: 210kPa

[0180] Longitudinal load: 6.08kN

[0181] Wet performance of new tires (WET-NEW)

[0182] A new prototype tire was assembled onto a rim (size = 19×7J) and filled with air to adjust the internal pressure of the tire to 230 kPa. The tire was then mounted on a test vehicle (a Japanese SUV). The test vehicle was driven through a fixed curve on a test course with a wet surface (water film thickness = 1.4 mm) and its maximum speed was measured. The results are shown in the "WET (NEW)" column of Tables 1 and 2 below, with Comparative Example 1 as 100. The larger the value, the higher the maximum speed, and the more superior the tire's wet performance.

[0183] Wet performance of worn tires (WET-OLD)

[0184] A new trial tire was assembled on a rim (size = 19×7J), and the internal pressure of the tire was adjusted to 230 kPa by filling it with air. The tire was mounted on a test vehicle (SUV car produced in Japan). The test vehicle was driven on a test route on a dry asphalt road surface to wear out the tread of each tire. The tread was worn out until the groove depth of the circumferential groove reached 50% of the groove depth of the new tire. Afterwards, the test vehicle was driven on a test route on a wet road surface (water film thickness = 1.4 mm) at a fixed turn, and the maximum speed was measured. The results are shown in the "WET (OLD)" column of Tables 1 and 2 below as an index with Comparative Example 1 as 100. The larger the value, the higher the maximum speed and the more superior the tire is in wet performance.

[0185] Table 1

[0186]

[0187] Table 2

[0188]

[0189] As shown in Table 1-2, in the examples, it has been confirmed that it is possible to achieve both reduced rolling resistance and improved wet performance. This evaluation result demonstrates the superiority of the present invention.

[0190] Industrial availability

[0191] The above-mentioned technology capable of reducing rolling resistance while improving wet performance can also be applied to various tires.

Claims

1. A tire having a tread forming a tread surface, characterized in that The orientation of the tread relative to the vehicle is specified, Of the two ends of the tread, the end provided on the inner side in the width direction of the vehicle is a first end, and the end provided on the outer side is a second end. The tread includes: a base layer; an intermediate layer located radially outside the base layer and covering the base layer; and a crown layer located radially outside the intermediate layer and covering the intermediate layer. The crown layer includes the tread surface, The loss tangent of the middle layer at 30°C is lower than that of the crown layer at 30°C, and the loss tangent of the base layer at 30°C is lower than that of the middle layer at 30°C. At least three circumferential grooves are engraved on the tread to form at least four land portions. The tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, the camber angle of the tire is set to -1°, a load of 50% of the regular load is applied to the tire, and the contact surface obtained by the tire contacting a flat road surface is used as a reference contact surface. In the reference ground contact surface, the land portion with the longest ground contact length is the longest land portion, and the land portion with the shortest ground contact length is the shortest land portion. a ratio of the thickness of the intermediate layer in the longest land portion to the thickness of the intermediate layer in the shortest land portion is greater than 1.0 and less than or equal to 3.5, When the tire is mounted on a vehicle, the longest land portion is formed on the inner tread provided on the inner side, and the shortest land portion is formed on the outer tread provided on the outer side.

2. The tire according to claim 1, wherein The intermediate layer is thicker on the first end side and thinner on the second end side.

3. The tire according to claim 2, characterized in that The tire was mounted on a regular rim, the internal pressure of the tire was adjusted to 230 kPa, and a load of 70% of the regular load was applied to the tire with the camber angle of the tire set to 0°. The ground contact surface obtained by making the tire contact a flat road surface was used as the reference ground contact surface. In the reference ground plane, the ratio of the axial width of the thick region of the intermediate layer to the ground width of the reference ground plane is 40% or more and 100% or less. The axial width is represented by an axial distance from a boundary where the ratio of the thickness of the intermediate layer to the total thickness of the intermediate layer and the crown layer is 50% to the reference ground contact end on the first end side.

4. The tire according to any one of claims 1 to 3, characterized in that The tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and when no load is applied to the tire, in a meridian cross-section of the tire, the contour of the tread surface is formed by an arc and represented by a plurality of curved contour lines arranged in parallel in the axial direction. The central curved contour line among the plurality of curved contour lines is a central curved contour line. The radius of the center curve contour line is greater than or equal to 500 mm and less than or equal to 1000 mm.

5. The tire according to any one of claims 1 to 3, characterized in that A ratio of a loss tangent of the crown layer at 30° C. to a loss tangent of the intermediate layer at 30° C. is not less than 125% and not more than 200%.

6. The tire according to claim 4, characterized in that A ratio of a loss tangent of the crown layer at 30° C. to a loss tangent of the intermediate layer at 30° C. is not less than 125% and not more than 200%.

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