tire

Abstract

To provide a tire 2 capable of achieving reduction of rolling resistance while preventing remarkable deterioration of wet performance caused by wear.SOLUTION: A tread 4 of a tire 2 is composed of a first tread 50 located on a first end TE1 side, and a second tread 52 located on a second end TE2 side. The first tread 50 comprises a first outer layer 54, an interposition layer 56, and a first inner layer 58. The second tread 52 comprises a second outer layer 60 and a second inner layer 62. The first outer layer 54 is composed of a cap layer 44. The interposition layer 56 and the second outer layer 60 are composed of the intermediate layer 46 whose loss tangent is lower than the loss tangent of the cap layer 44. The first inner layer 58 and the second inner layer 62 are composed of a base layer 48 whose loss tangent is lower than the loss tangent of the intermediate layer 46. In the first tread 50, a ratio of the thickness of the first outer layer 54 to the sum of the thicknesses of the first outer layer 54 and the interposition layer 56 is between 0.50 and 0.70.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] When low heat generation rubber is used in the tread, a tire with low rolling resistance is obtained. The grip of low heat generation rubber is inferior to that of high heat generation rubber that can exert a high grip. For this reason, when low heat generation rubber is used in the tread, for example, braking performance on wet road surfaces (hereinafter also referred to as wet performance) decreases. It is difficult to achieve a good balance between rolling resistance and wet performance. Various studies have been conducted with the aim of reducing rolling resistance and improving wet performance (for example, Patent Document 1 below).

[0003] For example, the tread of a tire disclosed in Patent Document 1 below is made up of three layers laminated in the radial direction. Of these three layers, the first layer (hereinafter also referred to as the cap layer) located on the outside is made of rubber that generates heat most easily, taking into consideration wet performance. The third layer (hereinafter also referred to as the base layer) located on the inside is made of rubber that generates heat least easily, taking into consideration rolling resistance. The second layer (hereinafter also referred to as the intermediate layer) located between the first and third layers is made of rubber that generates heat less easily than the first layer and more easily than the third layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-210044 A Summary of the Invention [Problem to be solved by the invention]

[0005] Considering the environment, there is a demand for further reduction in rolling resistance of tires. If the aforementioned intermediate layer is made of rubber that is less likely to heat up than conventional rubber, it is possible to reduce rolling resistance. However, rubber that is less likely to heat up has inferior grip. If the intermediate layer is made of rubber that is less likely to heat up, the gap between the grip of the cap layer and the grip of the intermediate layer will widen. In this case, there is a concern that wet performance will decrease significantly when the tread wears and the contact surface with the road surface changes from the cap layer to the intermediate layer.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a tire that can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear. [Means for solving the problem]

[0007] A tire according to one aspect of the present invention includes a tread that comes into contact with a road surface. The tread includes a cap layer, an intermediate layer having a loss tangent at 30°C lower than that of the cap layer at 30°C, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer at 30°C. The orientation of the tread with respect to the vehicle is specified, and of both ends of the tread, the end located on the outside in the width direction of the vehicle is a first end, and the end located on the inside is a second end. The tread is composed of a first tread located on the first end side and a second tread located on the second end side. The first tread includes a first outer layer, an intermediate layer located radially inside the first outer layer, and a first inner layer located radially inside the intermediate layer. The second tread includes a second outer layer and a second inner layer located radially inside the second outer layer. The first outer layer is made of the cap layer. The intermediate layer and the second outer layer are made of the intermediate layer. The first inner layer and the second inner layer are formed of the base layer. In the first tread, a ratio of a thickness of the first outer layer to a total thickness of the first outer layer and the intermediate layer is 0.50 or more and 0.70 or less.

[0008] Preferably, in the tire, at least three circumferential grooves are cut in the tread in parallel in the axial direction, and among the at least three circumferential grooves, a circumferential groove located on an outer side in the axial direction is a shoulder circumferential groove. The shoulder circumferential groove is cut in the first tread.

[0009] Preferably, in the tire, a ratio of a loss tangent at 30° C. of the intermediate layer to a loss tangent at 30° C. of the cap layer is greater than or equal to 0.50 and is less than or equal to 0.70.

[0010] Preferably, in this tire, the standard contact surface is obtained by mounting the tire on a regular rim, adjusting the internal pressure of the tire to 230 kPa, and placing a load of 70% of the regular load as a vertical load on the tire with a camber angle of -1°, and bringing the tire into contact with a flat road surface. The standard contact length is the contact length measured at a position corresponding to 80% of the contact width of the standard contact surface, the standard contact length on the first end side is the first standard contact length, and the standard contact length on the second end side is the second standard contact length. The ratio of the first standard contact length to the second standard contact length is 0.60 or more and 0.90 or less.

[0011] Preferably, in the tire, in a meridian cross section of the tire when the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and no load is applied to the tire, the outer surface of the tire comprises a tread surface and a pair of side surfaces continuous with the ends of the tread surface. The contour of the tread surface includes a curved contour line that passes through the equator of the tire and is made of a circular arc. The radius of the curved contour line is 500 mm or more and 1000 mm or less.

[0012] Preferably, in the tire, the first tread includes a terminal portion penetrating the intermediate layer and the first inner layer. The terminal portion is electrically conductive. Effect of the Invention

[0013] According to the present invention, it is possible to obtain a tire that can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the contour of a shoulder portion of a tire. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing a portion of the tread. [Figure 4] FIG. 4 is an image diagram explaining the camber angle of a tire. [Diagram 5] FIG. 5 is an image diagram for explaining the standard contact length of the standard contact surface. [Figure 6] FIG. 6 is a cross-sectional view showing the contour of the tread surface. [Figure 7] FIG. 7 is a cross-sectional view showing a portion of a tire according to another embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view showing a part of the tire of Comparative Example 1. As shown in FIG. [Figure 9] FIG. 9 is a cross-sectional view showing a part of the tire of Comparative Example 2. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0016] In this disclosure, a 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 a standard state. A state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, and no load is applied to the tire is referred to as a standard state.

[0017] In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in a meridian section of the tire that cannot be measured when the tire is mounted on a normal rim are measured by cutting the tire along a plane including the rotation axis, and the distance between the left and right beads in the tire section is measured so as to match the distance between the beads in the tire mounted on a normal rim.

[0018] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0019] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0020] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0021] In the present disclosure, the crosslinked rubber is a molded product of the rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0022] Examples of the base rubber include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of the base rubber and chemicals, the content of the selected chemicals, etc. are appropriately determined depending on the specifications of each element such as the tread and sidewall to which the rubber composition is applied.

[0023] In this disclosure, conductive rubber has a volume resistivity of 1.0×10 8 Non-conductive rubber means crosslinked rubber with a volume resistivity of less than 1.0×10 8 It means crosslinked rubber with a conductivity of Ω·cm or more. The conductivity of rubber is usually controlled by the content of carbon black. The main component of the reinforcing agent in conductive rubber is carbon black, and the main component of the reinforcing agent in non-conductive rubber is silica.

[0024] In the present disclosure, when the rubber composition contains silica and carbon black as reinforcing agents, if the silica content, expressed as the ratio of the amount of silica to the total amount of the reinforcing agent, expressed as the sum of the amount of silica and the amount of carbon black, is 50 mass% or more, silica is the main component of the reinforcing agent.

[0025] In this disclosure, the amount of chemicals blended is expressed in parts by mass of chemicals per 100 parts by mass of base rubber.

[0026] In the present disclosure, the volume resistivity of an element made of crosslinked rubber among the elements constituting a tire is measured in accordance with the double ring electrode method specified in JIS K6271 at a temperature of 25° C. For this measurement, a sheet (thickness=2 mm) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170° C. for 12 minutes is used.

[0027] In the present disclosure, the loss tangent (also referred to as tan δ) at a temperature of 30°C of an element made of crosslinked rubber among the elements constituting a tire is measured in accordance with the provisions of JIS K6394 using a viscoelasticity spectrometer ("IPLEXER series" manufactured by GABO Corporation) under the following conditions. Initial distortion = 10% Dynamic strain = 1% Frequency = 10Hz Deformation mode = tension In this measurement, a test piece (length = 20 mm, width = 4 mm, thickness = 1 mm) is sampled from the tire. In this sampling, the length direction of the test piece is aligned with the circumferential direction of the tire, and the thickness direction of the test piece is aligned with the radial direction of the tire. When it is not possible to sample a test piece from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes.

[0028] In the present disclosure, the LAT abrasion index is an index for evaluating the abrasion resistance of an element made of crosslinked rubber among elements constituting a tire. The higher the LAT abrasion index, the more excellent the abrasion resistance of the element being evaluated. The LAT abrasion index corresponds to the abrasion resistance index defined in JIS K6264, and is expressed as the ratio of the abrasion volume of a reference sample to the abrasion volume of an evaluation sample. The abrasion volume is measured, for example, under conditions of a load of 40N and a slip angle of 6° using an abrasion tester (for example, LAT100 abrasion tester manufactured by VMI). The reference sample is appropriately set according to the elements to be evaluated.

[0029] Fig. 1 shows a portion of a tire 2 according to one embodiment of the present invention. This tire 2 is a tire for passenger cars. Fig. 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. In Fig. 1, 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. The direction perpendicular to the paper surface of Fig. 1 is the circumferential direction of the tire 2.

[0030] 1, the dashed dotted line EL is the equatorial plane of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane, except for the tread pattern, decorations such as designs and letters engraved on the outer surface, and the internal structure of the tread, which will be described later.

[0031] In FIG. 1, a tire 2 is mounted on a rim R. The rim R is a regular rim. Air is filled inside the tire 2, and the internal pressure of the tire 2 is adjusted. The tire 2 mounted on the rim R is also called a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on the rim R.

[0032] 1, the position indicated by the symbol PW is the axially outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the outer end PW is identified based on a virtual outer surface obtained by assuming that there is no decoration.

[0033] In Fig. 1, the length indicated by the symbol WA is the maximum width of the tire 2, i.e., the section width (see JATMA, etc.). The section 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 position where the tire 2 shows the maximum width (hereinafter, the maximum width position). The section width WA is measured with the tire 2 in a standard state.

[0034] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinches 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a band 16 , a pair of chafers 18 , and an inner liner 20 .

[0035] The outer surface of the tread 4 comes into contact with the road surface. Grooves 22 are cut into the tread 4. This forms a tread pattern.

[0036] The grooves 22 constituting the tread pattern include circumferential grooves 24 that extend continuously in the circumferential direction. In this tire 2, at least three circumferential grooves 24 arranged in parallel in the axial direction are cut into the tread 4. As a result, at least four land portions 26 are formed in the tread 4. In the tire 2 shown in FIG. 1, five land portions 26 are formed by cutting the four circumferential grooves 24 into the tread 4.

[0037] The tread 4 of this tire 2 includes a tread body 28 and a pair of wings 30. Each of the wings 30 is located axially outward of the tread body 28. The wings 30 join the tread body 28 and the sidewall 6. The wings 30 are made of crosslinked rubber with adhesive properties taken into consideration.

[0038] In FIG. 1, the position indicated by the symbol TE is an end of the tread 4. In this tire 2, the orientation of the tread 4 with respect to the vehicle is specified. The end TE of the tread 4 located on the left side of the paper in FIG. 1 is the first end TE1, and the end TE of the tread 4 located on the right side is the second end TE2. When this tire 2 is mounted on a vehicle, of both ends TE of the tread 4, the first end TE1 of the tread 4 is positioned on the outer side in the width direction of the vehicle. The second end TE2 of the tread 4 is positioned on the inner side in the width direction of the vehicle.

[0039] 1, the position indicated by the reference symbol PE is the equator of the tire 2. The equator PE is the intersection point between the outer surface of the tread 4 and the equatorial plane. If a groove 22 is present on the equatorial plane, the equator PE is determined based on a virtual outer surface of the tread 4 obtained by assuming that the groove 22 does not exist.

[0040] 1, the position indicated by the symbol PH is a position on the outer surface of the tread 4. The position PH corresponds to the axially outer end of the contact surface of the tire 2 with the road surface.

[0041] The contact patch for identifying the position PH is obtained, for example, by using a contact patch shape measuring device (not shown). This contact patch is obtained by applying a load of 70% of the normal load as a vertical load to the tire 2 with the camber angle of the tire 2 in a standard state set to 0°, and bringing the tire 2 into contact with a flat road surface. Although not shown, in the tire 2, the contact patch obtained in this manner is the reference contact patch, and the position on the outer surface of the tread 4 corresponding to the axial outer end of this reference contact patch is the above-mentioned position PH. In the tire 2, this position PH is the reference contact edge. In FIG. 1, the length indicated by the symbol WH is the contact width of the reference contact patch. The contact width WH is the axial distance from one reference contact edge PH to the other reference contact edge PH. The contact width WH is measured at the reference contact patch.

[0042] Each sidewall 6 is continuous with an 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 toward the clinch 8 along the carcass 12. The sidewall 6 is made of crosslinked rubber in consideration of cut resistance.

[0043] Each clinch 8 is located radially inside the sidewall 6. The clinch 8 contacts the rim R. The clinch 8 is made of crosslinked rubber in consideration of wear resistance.

[0044] Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 32 and an apex 34. Although not shown, the core 32 includes a steel wire.

[0045] The apex 34 is located radially outward of the core 32. The apex 34 tapers outward. The apex 34 is made of crosslinked rubber having high rigidity.

[0046] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between one bead 10 and the other bead 10. This carcass 12 has a radial structure.

[0047] 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 on the inner side 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 viewpoint of weight reduction, the carcass 12 may be composed of one carcass ply 36.

[0048] The first carcass ply 38 includes a first ply body 38a that spans between one core 32 and the other core 32, and a pair of first turn-up portions 38b that are connected to the first ply body 38a and are turned back from the axial inside to the axial outside around each core 32.

[0049] The second carcass ply 40 includes a second ply body 40a that spans between one core 32 and the other core 32, and a pair of second turn-up portions 40b that are connected to the second ply body 40a and are turned up from the axially inner side to the axially outer side around each core 32.

[0050] Although not shown, the carcass ply 36 includes a number of carcass cords arranged in parallel. Each carcass cord crosses the equator plane. The carcass cord is a cord made of an organic fiber. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0051] The belt 14 is located on the inside of the tread 4 in the radial direction. The belt 14 is layered on the carcass 12 from the outside in the radial direction. In FIG. 1, the length indicated by the symbol WR is the axial width of the belt 14. The axial width WR is the axial distance from one end of the belt 14 to the other end. In this tire 2, the axial width WR of the belt 14 is 65% or more and 85% or less of the cross-sectional width WA.

[0052] The belt 14 is composed of at least two layers 42 laminated in the radial direction. The belt 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. As shown in FIG. 1, the inner layer 42a is wider than the outer layer 42b. The length from an end of the outer layer 42b to an end of the inner layer 42a is 3 mm or more and 10 mm or less.

[0053] Although not shown, each of the inner layer 42a and the outer layer 42b includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equator plane. The material of the belt cord is steel.

[0054] The band 16 is located between the tread 4 and the belt 14 in the radial direction. The band 16 is laminated on the belt 14 on the inside of the tread 4.

[0055] Although not shown, the band 16 includes a band cord wound in a spiral shape. The band cord extends substantially in the circumferential direction. Specifically, the angle that the band cord forms with the circumferential direction is 5° or less. The band 16 has a jointless structure. In the tire 2, a cord made of an organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0056] The band 16 of the tire 2 is composed of a full band whose two ends face each other across the equator PE. The band 16 is wider than the belt 14. The length from the end of the belt 14 to the end of the band 16 is 3 mm or more and 7 mm or less. The band 16 covers the entire belt 14. The band 16 may include a pair of edge bands that are spaced apart in the axial direction and cover the ends of the full band and the ends of the belt 14. The band 16 may be composed of only a pair of edge bands.

[0057] Each chafer 18 is located radially inside the bead 10. The chafers 18 contact the rim R. The chafers 18 of the tire 2 are made of cloth and rubber impregnated into the cloth.

[0058] The inner liner 20 is positioned inside the carcass 12. The inner liner 20 constitutes the inner surface of the tire 2. The inner liner 20 is made of a crosslinked rubber having a low gas permeability coefficient. The inner liner 20 maintains the internal pressure of the tire 2.

[0059] Fig. 2 shows a part of the tire 2 shown in Fig. 1. In Fig. 2, 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. The direction perpendicular to the paper surface of Fig. 2 is the circumferential direction of the tire 2.

[0060] Fig. 2 shows the outline of the shoulder portion of the tire 2 in a meridian cross section. The outline shown in Fig. 2 is obtained by measuring the outer surface shape of the tire 2 in a standard state with a displacement sensor. Fig. 2 shows the outline of the outer surface of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0061] In a meridian cross section, the contour of the outer surface of the tire 2 (hereinafter, tire outer surface TS) is formed by connecting multiple contour lines consisting of straight lines or circular arcs. In this disclosure, a contour line consisting of a straight line or a circular arc is simply referred to as a contour line. A contour line consisting of a straight line is referred to as a straight contour line, and a contour line consisting of a circular arc is referred to as a curved contour line.

[0062] The tire outer surface TS includes a tread surface T and a pair of side surfaces S connected to the ends of the tread surface T. In a meridian cross section, the contour of the tread surface T includes a plurality of curved contour lines having different radii. In this tire 2, the curved contour line having the smallest radius among the plurality of curved contour lines included in the contour of the tread surface T is located at the end portion of the tread surface T and connected to the side surface S. In a meridian cross section, the contour of the tire outer surface TS includes a curved portion, which is a curved contour line consisting of an arc having the smallest radius among the plurality of curved contour lines included in the contour of the tread surface T and connected to the side surface S, at the end portion of the tread surface T. In FIG. 2, this curved portion is indicated by the symbol RS.

[0063] In the contour of the tire outer surface TS, the curved portion RS is tangent to a contour line adjacent to the axially inner side (hereinafter, referred to as an inner adjacent contour line NT) at a tangent point CT. This curved portion RS is tangent to a contour line constituting the contour of the side surface S adjacent to the axially outer side (hereinafter, referred to as an outer adjacent contour line NS) at a tangent point CS. This contour of the tire outer surface TS includes an inner adjacent contour line NT located axially inside the curved portion RS and tangent to the curved portion RS, and an outer adjacent contour line NS located axially outside the curved portion RS and tangent to the curved portion RS.

[0064] In Fig. 2, a solid line LT is a tangent to the curved portion RS at a contact point CT between the inner adjacent contour line NT and the curved portion RS. A solid line LS is a tangent to the curved portion RS at a contact point CS between the outer adjacent contour line NS and the curved portion RS. The position indicated by the symbol PT is the intersection point between the tangent line LT and the tangent line LS. In this tire 2, this intersection point PT is the tread reference edge.

[0065] In Fig. 1, the length indicated by the double-headed arrow 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-sectional width WA (WT / WA) is 70% or more and 90% or less. The ratio of the contact width WH of the reference contact surface to the tread width WT is 70% or more and 90% or less.

[0066] As described above, the four circumferential grooves 24 are formed in the tread 4 of the tire 2. There are no particular limitations on the arrangement, groove depth, and groove width of the four circumferential grooves 24 in the tire 2. The arrangement, groove depth, and groove width of the circumferential grooves of a tire are generally applied to the tread 4.

[0067] In the tire 2, of the four circumferential grooves 24, the circumferential groove 24 located on the outer side in the axial direction is a shoulder circumferential groove 24s. The circumferential groove 24 located on the inner side of the shoulder circumferential groove 24s is a middle circumferential groove 24m. In the tire 2, the four circumferential grooves 24 are configured with a pair of shoulder circumferential grooves 24s and a pair of middle circumferential grooves 24m. The pair of shoulder circumferential grooves 24s and the pair of middle circumferential grooves 24m are disposed symmetrically with respect to the equatorial plane. These circumferential grooves 24 may be disposed asymmetrically with respect to the equatorial plane.

[0068] 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 on the outer side in the axial direction is the shoulder land portion 26s. The land portion 26 located on the inner side of the shoulder land portion 26s in the axial direction 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.

[0069] In FIG. 1, the length indicated by the double arrow WC is the axial width of the center land portion 26c. The axial width WC is represented by the axial distance from the boundary between the middle circumferential groove 24m on the first end TE1 side and the outer surface of the center land portion 26c to the boundary between the middle circumferential groove 24m on the second end TE2 side and the outer surface of the center land portion 26c. The length indicated by the double arrow WM is the axial width of the middle land portion 26m. The axial width WM is represented by the axial distance from the boundary between the middle circumferential groove 24m and the outer surface of the middle land portion 26m to the boundary between the shoulder circumferential groove 24s and the outer surface of the middle land portion 26m. The length indicated by the double arrow WS is the axial width of the shoulder land portion 26s. The axial width WS is represented by the axial distance from the boundary between the shoulder circumferential groove 24s and the outer surface of the shoulder land portion 26s to the tread reference end PT.

[0070] In the tire 2, from the viewpoint of achieving a good balance between steering stability and drainage, the ratio (WC / WT) of the axial width WC of the center land portion 26c to the tread width WT is preferably 0.08 or more and 0.20 or less. The ratio (WS / WT) of the axial width WS of the shoulder land portion 26s to the tread width WT is preferably 0.20 or more and 0.30 or less. The ratio (WM / WT) of the axial width WM of the middle land portion 26m to the tread width WT is set in consideration of the ratios (WC / WT) and (WS / WT).

[0071] The tread 4 (more specifically, the tread body 28) of the tire 2 includes a cap layer 44, an intermediate layer 46, and a base layer 48. The cap layer 44, the intermediate layer 46, and the base layer 48 are each made of a crosslinked rubber having a different heat generation property. In the tire 2, the loss tangent LTm of the intermediate layer 46 at 30°C is lower than the loss tangent LTc of the cap layer 44 at 30°C. The loss tangent LTb of the base layer 48 at 30°C is lower than the loss tangent LTm of the intermediate layer 46 at 30°C. In the tire 2, the cap layer 44 is most susceptible to heat generation and contributes to the exertion of the grip force of the tire 2. The base layer 48 is least susceptible to heat generation and contributes to the reduction of the rolling resistance of the tire 2.

[0072] The intermediate layer 46 of this tire 2 has heat generation properties between those of the cap layer 44 and those of the base layer 48. By configuring the intermediate layer 46 to have a loss tangent LTm close to the loss tangent LTc of the cap layer 44, a tread 4 that prioritizes exerting grip force is obtained. By configuring the intermediate layer 46 to have a loss tangent LTm close to the loss tangent LTb of the base layer 48, a tread 4 that prioritizes reducing rolling resistance is obtained.

[0073] 1, the tread body 28 of the tire 2 is composed of a three-layer laminate on the first end TE1 side, and is composed of a two-layer laminate on the second end TE2 side. In the tire 2, the portion including the three-layer laminate on the first end TE1 side is a first tread 50, and the portion including the two-layer laminate on the second end TE2 side is a second tread 52. The tread 4 is composed of the first tread 50 located on the first end TE1 side, and the second tread 52 located on the second end TE2 side.

[0074] In Fig. 1, the position indicated by the symbol PB is the boundary between the first tread 50 and the second tread 52 on the tread surface T. In Fig. 1, the length indicated by the double-headed arrow WT1 is the axial distance from the reference ground contact end PH on the first end TE side to the boundary PB.

[0075] The first tread 50 includes a first outer layer 54, an intermediate layer 56, and a first inner layer 58. The outer surface of the first outer layer 54 forms a part of the tread surface T described above. The intermediate layer 56 is located radially inward of the first outer layer 54. The first inner layer 58 is located radially inward of the intermediate layer 56. As shown in FIG. 1 , the first outer layer 54 is laminated to the intermediate layer 56. The intermediate layer 56 is laminated to the first inner layer 58. The first inner layer 58 is laminated to the band 16.

[0076] The second tread 52 includes a second outer layer 60 and a second inner layer 62. The outer surface of the second outer layer 60 forms a part of the tread surface T described above. The second inner layer 62 is located radially inside the second outer layer 60. As shown in FIG. 1 , the second outer layer 60 is laminated to the second inner layer 62. The second inner layer 62 is laminated to the band 16.

[0077] In the tire 2, the first outer layer 54 of the first tread 50 is composed of the cap layer 44. The intermediate layer 56 of the first tread 50 and the second outer layer 60 of the second tread 52 are composed of the intermediate layer 46. The first inner layer 58 of the first tread 50 and the second inner layer 62 of the second tread 52 are composed of the base layer 48.

[0078] In the tire 2, the second tread 52 includes a terminal portion 64 made of conductive rubber. The terminal portion 64 penetrates the second outer layer 60 and the second inner layer 62 of the second tread 52. An outer end of the terminal portion 64 forms a part of the tread surface T. The terminal portion 64 is connected to the band 16 at an inner end. The terminal portion 64 contributes to ensuring electrical conductivity of the tire 2.

[0079] As described above, the tread 4 comes into contact with the road surface and contributes to exerting grip force. The contribution of the tread 4 to the grip force is greater on the first end TE1 side than on the second end TE2 side of the tread 4.

[0080] The tread surface T of this tire 2 includes a portion made of an intermediate layer 46 that is disadvantageous in exerting grip force. However, in this tire 2, the first outer layer 54 of the first tread 50 on the first end TE1 side is made of a cap layer 44 that takes into consideration the exertion of grip force. In this tire 2, even though the tread surface T includes a portion made of an intermediate layer 46 that is disadvantageous in exerting grip force, the tread 4 contributes to the exertion of grip force. In this tire 2, good wet performance is ensured. Since it is possible to configure the tread 4 to include a large amount of the intermediate layer 46 that can contribute to reducing rolling resistance, this tire 2 can reduce rolling resistance.

[0081] As shown in Fig. 1, in this tire 2, of the four circumferential grooves 24 cut in the tread 4, a shoulder circumferential groove 24s located on the outer side in the axial direction is cut in a first tread 50. Fig. 3 shows a part of a cross section of the tire 2 shown in Fig. 1. Fig. 3 shows a part of the shoulder circumferential groove 24s cut in the first tread 50. A slip sign 66 (also referred to as a wear indicator) is provided at the bottom of the shoulder circumferential groove 24s.

[0082] In FIG. 3, the double-headed arrow TG indicates the thickness of the first outer layer 54. The double-headed arrow TK indicates the thickness of the intermediate layer 56. The double-headed arrow TC indicates the total thickness of the thickness TG of the first outer layer 54 and the thickness TK of the intermediate layer 56. The thickness TG of the first outer layer 54, the thickness TK of the intermediate layer 56, and the total thickness TC are measured in a portion where the change in thickness of each layer is suppressed within a zone up to a position 5 mm away from the boundary between the outer surface of the land portion 26 and the circumferential groove 24 (in other words, the edge of the circumferential groove 24). In addition, when a plurality of circumferential grooves 24 are engraved in the first tread 50, the thickness of the first outer layer 54, the thickness of the intermediate layer 56, and the total thickness are measured in each circumferential groove 24, and the thickness TG of the first outer layer 54, the thickness TK of the intermediate layer 56, and the total thickness TC are expressed based on the average values ​​thereof.

[0083] In the tire 2, in the first tread 50, the ratio (TG / TC) of the thickness TG of the first outer layer 54 to the total thickness TC of the thickness TG of the first outer layer 54 and the thickness TK of the intermediate layer 56 is 0.50 or greater and 0.70 or less.

[0084] Since the ratio (TG / TC) is 0.50 or greater, a sufficient thickness of the first outer layer 54 that contributes to exerting grip force is ensured. A significant decrease in wet performance due to wear is suppressed in the tire 2. From this viewpoint, the ratio (TG / TC) is preferably 0.53 or greater, and more preferably 0.55 or greater.

[0085] Since the ratio (TG / TC) is 0.70 or less, the thickness of the intermediate layer 56 made of the intermediate layer 46, which contributes to reducing rolling resistance, is effectively ensured. In the tire 2, the influence on rolling resistance of the first outer layer 54 made of the cap layer 44, which is prone to heat generation, is suppressed. From this viewpoint, the ratio (TG / TC) is preferably 0.67 or less, and more preferably 0.65 or less.

[0086] In this tire 2, the first tread 50 on the first end TE1 side has a first outer layer 54 made of a cap layer 44, and a ratio (TG / TC) of a thickness TG of this first outer layer 54 to a total thickness TC of the thickness TG of the first outer layer 54 and a thickness TK of the intermediate layer 56 is 0.50 or more and 0.70 or less. This tire 2 can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear.

[0087] 3, the double-headed arrow DG indicates the groove depth of the circumferential groove 24. This groove depth DG is represented by the distance from the tread surface T to the slip sign 66. This groove depth DG is also called the effective groove depth.

[0088] In this tire 2, from the viewpoint of achieving a good balance between wet performance and rolling resistance, the ratio (TC / DG) of the total thickness TC of the thickness TG of the first outer layer 54 and the thickness TK of the intermediate layer 56 to the groove depth DG of the circumferential groove 24 is preferably 0.80 or greater and 1.00 or less.

[0089] As shown in FIG. 1, in the tire 2, the position of the end of the first outer layer 54 on the first end TE1 side (hereinafter, the first end 68a of the first outer layer 54) is located outside the reference ground contact edge PH in the axial direction. The position of the first end 68a of the first outer layer 54 almost coincides with the position of the tread reference edge PT in the axial direction. The first end 68a of the first outer layer 54 may be located inside the tread reference edge PT in the axial direction. In this case, from the viewpoint of effectively exerting wet performance, the axial distance from the tread reference edge PT to the first end 68a of the first outer layer 54 is preferably 5 mm or less. The first end 68a of the first outer layer 54 may be located outside the tread reference edge PT in the axial direction. In this case, the position of the first end 68a of the first outer layer 54 is determined taking into consideration the influence on wet performance and rolling resistance.

[0090] 1, in the tire 2, of the four circumferential grooves 24 formed in the tread 4, a shoulder circumferential groove 24s located on the outer side in the axial direction is formed in the first tread 50. A boundary PB between the first tread 50 and the second tread 52, i.e., an end of the first outer layer 54 located on the second end TE2 side (hereinafter, a second end 68b of the first outer layer 54) is located on the outer side of the shoulder circumferential groove 24s located on the first end TE side in the axial direction.

[0091] As described above, in the tire 2, the position of the first end 68a of the first outer layer 54 substantially coincides with the position of the tread reference end PT in the axial direction. In the tread 4, the portion between the tread reference end PT and the shoulder circumferential groove 24s is the shoulder land portion 26s. In the tire 2, the outer surface of the shoulder land portion 26s on the first end TE1 side, which contributes greatly to the grip force, is mostly formed of the first outer layer 54. In the tire 2, good wet performance is ensured.

[0092] In this tire 2, wet performance and rolling resistance can be controlled by adjusting the position of the boundary PB between the first tread 50 and the second tread 52. By bringing the boundary PB closer to the first end TE1 of the tread 4, the rolling resistance of the tire 2 can be reduced. From this viewpoint, the ratio (WT1 / WH) of the axial distance WT1 from the reference ground contact end PH on the first end TE1 side to the boundary PB to the contact width WH of the reference ground contact surface is preferably 95% or less, and more preferably 85% or less. On the other hand, by bringing the boundary PB closer to the second end TE2 of the tread 4, the wet performance of the tire 2 can be improved. From this viewpoint, the ratio (WT1 / WH) is preferably 30% or more, and more preferably 40% or more. From the viewpoint of achieving a good balance between wet performance and rolling resistance, the ratio (WT1 / WH) is particularly preferably 55% or more and 75% or less.

[0093] As described above, the loss tangent LTm of the intermediate layer 46 at 30° C. is lower than the loss tangent LTc of the cap layer 44 at 30° C. Specifically, the ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 46 at 30° C. to the loss tangent LTc of the cap layer 44 at 30° C. is preferably 0.50 or more and 0.70 or less.

[0094] Setting the ratio (LTm / LTc) to be 0.50 or greater effectively suppresses the deviation between the grip force of the cap layer 44 and the grip force of the intermediate layer 46. A significant decrease in wet performance due to wear is suppressed in the tire 2. From this viewpoint, the ratio (LTm / LTc) is more preferably 0.53 or greater, and further preferably 0.55 or greater.

[0095] Setting the ratio (LTm / LTc) to be equal to or less than 0.70 allows the mid layer 46 to effectively contribute to reducing rolling resistance. From this viewpoint, the ratio (LTm / LTc) is preferably equal to or less than 0.67, and more preferably equal to or less than 0.65.

[0096] In this tire 2, the loss tangent LTb of the base layer 48 at 30° C. is preferably 0.11 or less. This is because the base layer 48 effectively contributes to reducing rolling resistance. From this viewpoint, the loss tangent LTb is more preferably 0.10 or less, and further preferably 0.09 or less. In this tire 2, the smaller the loss tangent LTb of the base layer 48, the more preferable it is, and therefore no preferable lower limit is set.

[0097] 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 contributes to reducing rolling resistance. From this viewpoint, the loss tangent Ltm is more preferably 0.14 or less, and even more preferably 0.13 or less. The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.11 or more. This is because the intermediate layer 46 can ensure the necessary rigidity and can effectively contribute to improving wet performance. From this viewpoint, the loss tangent LTm is more preferably 0.12 or more.

[0098] The loss tangent LTc of the cap layer 44 at 30°C is preferably 0.15 or more. This is because the cap layer 44 can contribute to improving wet performance. From this viewpoint, the loss tangent LTc is more preferably 0.16 or more, and even more preferably 0.17 or more. The cap layer 44 contacts the road surface. From the viewpoint of improving wet performance, the higher the loss tangent LTc, the more preferable. However, a high loss tangent LTc leads to heat generation. There is a concern that the heated cap layer 44 will increase the temperature of the intermediate layer 46 more than expected. From the viewpoint of keeping the temperature state of the entire tread 4 stable and maintaining low rolling resistance, the loss tangent LTc of the cap layer 44 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and even more preferably 0.27 or less.

[0099] Fig. 4 shows a state of the tire 2 mounted on a vehicle (not shown). In Fig. 4, the left side is the outer side in the width direction of the vehicle, and the right side is the inner side in the width direction of the vehicle.

[0100] As shown in FIG. 4, the tire 2 is usually mounted on a vehicle so that its equatorial plane EL is inclined with respect to the road surface. In FIG. 4, the solid line indicated by the symbol BL is a straight line perpendicular to the flat road surface. The angle θ is the angle that the equatorial plane EL makes with respect to this straight line BL. This angle θ is also called the camber angle. The tire 2 shown in FIG. 4 is mounted on a vehicle so that the upper part of the equatorial plane EL is located more inward than the lower part in the width direction of the vehicle. The camber angle of the tire 2 mounted in this way is also called negative camber and is expressed as a negative angle.

[0101] Fig. 5 shows an image of the contact surface of the tire 2. In Fig. 5, 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. The left side of Fig. 5 is the outer side in the width direction of the vehicle, in other words, the first end TE1 side of the tread 4. The right side of the page is the inner side in the width direction of the vehicle, in other words, the second end TE2 side of the tread 4.

[0102] This contact patch is obtained, for example, by using a contact patch shape measuring device (not shown). This contact patch is obtained by applying a load of 70% of the normal load as a vertical load to the tire 2 with the camber angle θ of the tire 2 in a standard state set to -1°, and bringing the tire 2 into contact with a flat road surface. In the present disclosure, this contact patch is the standard contact patch.

[0103] In FIG. 5, the dashed line CL is the axial center line of the standard contact patch. The solid line ML is a straight line that passes through the axial outer end of the standard contact patch and is parallel to the center line CL. The solid line AL is a straight line that is located between the straight line ML and the center line CL and is parallel to the straight line ML and the center line CL. The double-headed arrow A100 represents the axial distance from the center line CL to the straight line ML. This distance A100 corresponds to half of the maximum contact width of the standard contact patch. The double-headed arrow A80 represents the axial distance from the center line CL to the straight line AL. In this tire 2, the ratio of the distance A80 to the distance A100 is set to 80%. In other words, the straight line AL represents a position that corresponds to 80% of the maximum contact width of the standard contact patch. The double-headed arrow L is the length of the intersection line between the plane including the straight line AL and the standard contact patch. The length L of this intersection line is the contact length measured at a position that corresponds to 80% of the contact width of the standard contact patch, and is also called the standard contact length. The standard contact length L on the first end TE1 side is a first standard contact length L1, and the standard contact length on the second end TE2 side is a second standard contact length L2.

[0104] In the tire 2, the ratio (L1 / L2) of the first standard contact length L1 to the second standard contact length L2 is preferably equal to or greater than 0.60 and equal to or less than 0.90.

[0105] By setting the ratio (L1 / L2) to 0.60 or more, changes in the ground contact shape due to alignment are effectively suppressed. A stable ground contact shape is obtained, so the occurrence of uneven wear is suppressed. This tire 2 can achieve a reduction in rolling resistance while preventing a significant decrease in wet performance due to wear. From this viewpoint, the ratio (L1 / L2) is more preferably 0.65 or more, and even more preferably 0.70 or more.

[0106] By setting the ratio (L1 / L2) to be 0.90 or greater, the tread 4 can fully exhibit its functions. In this tire, cornering stability and straight-line stability are well balanced. This tire 2 can exhibit good wet performance while maintaining low rolling resistance. From this viewpoint, the ratio (L1 / L2) is more preferably 0.85 or less, and further preferably 0.80 or less.

[0107] Fig. 6 shows a part of the tire 2 shown in Fig. 1. In Fig. 6, 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. The direction perpendicular to the paper surface of Fig. 6 is the circumferential direction of the tire 2.

[0108] Fig. 6 shows the contour of the tread surface T of the tire 2 in a meridian cross section. The contour shown in Fig. 6, like the contour shown in Fig. 2, is obtained by measuring the outer surface shape of the tire 2 in a standard state with a displacement sensor. Fig. 6 shows the contour of the tread surface T of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0109] The tread surface T of the tire 2 is divided into a plurality of regions arranged in parallel in the axial direction in a meridian cross section. The plurality of regions include a crown region Cr, a pair of middle regions Mi, and a pair of side regions Sd. The crown region Cr is located at the center in the axial direction. The crown region Cr includes an equator PE. Each middle region Mi is located outside the crown region Cr in the axial direction. Each side region Sd is located outside the middle region Mi in the axial direction.

[0110] In Fig. 6, the position indicated by the symbol CM is the boundary between the crown region Cr and the middle region Mi. The position indicated by the symbol MS is the boundary between the middle region Mi and the side region Sd. The symbol SE is the outer end of the side region Sd. The outer end SE is also the aforementioned contact point CT.

[0111] As described above, the contour of the tread surface T includes a plurality of curved contours having different radii. The contour of each region is represented by a curved contour. In the tire 2, the curved contour representing the contour of the crown region Cr is also referred to as a center contour. The curved contour representing the contour of the middle region Mi is also referred to as a middle contour. The curved contour representing the contour of the side region Sd is also referred to as a side contour. The plurality of curved contours included in the contour of the tread surface T include a center contour, a pair of middle contours, and a pair of side contours.

[0112] Although not shown, the center of the center contour is located on the equatorial plane. In FIG. 6, the single arrow indicated by the symbol Rc is the radius of the center contour. The middle contour meets the center contour at the boundary CM. In FIG. 6, the single arrow indicated by the symbol Rm is the radius of the middle contour. The side contour meets the middle contour at the boundary MS. In FIG. 6, the single arrow indicated by the symbol Rd is the radius of the side contour.

[0113] 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 Rs of the side contour line is smaller than the radius Rm of the middle contour line. This allows each contour line to be smoothly connected to form a tread 4 that can fully exhibit its functions. In this tire, cornering stability and straight-line stability are well balanced. From this viewpoint, the ratio (Rm / Rc) of the radius Rm of the middle contour line to the radius Rc of the center contour line is preferably 0.50 or more and preferably 0.54 or less. The ratio (Rd / Rc) of the radius Rd of the side contour line to the radius Rc of the center contour line is preferably 0.20 or more and preferably 0.24 or less.

[0114] In the tire 2, the radius Rc of the center contour line is preferably 500 mm or more and 1000 mm or less. This allows a ground contact shape in which the ratio (L1 / L2) of the first standard ground contact length L1 to the second standard ground contact length L2 is set within the above-mentioned range to be obtained. Since the tread 4 can fully exert its function, the tire 2 can achieve a reduction in rolling resistance while preventing a significant decrease in wet performance due to wear. From this viewpoint, the radius Rc of the center contour line is more preferably 550 mm or more, and even more preferably 600 mm or more. The radius Rc of the center contour line is more preferably 950 mm or less, and even more preferably 900 mm or less. In the tire 2, the radius Rc of a circular arc having a center on the equatorial plane and passing through the left and right edges of the center land portion 26c and the equator PE is used as the radius Rc of the center contour line. In a tread in which a circumferential groove is engraved on the equatorial plane, the radius Rc of a circular arc having a center on the equatorial plane and passing through the edges of the land portions located on both sides of the circumferential groove is used as the radius Rc of the center contour line.

[0115] In this tire 2, the cap layer 44 and the intermediate layer 46 coexist in the first tread 50. If there is a discrepancy between the wear resistance of the cap layer 44 and the wear resistance of the intermediate layer 46, there is a concern that the wear amounts of the two will differ. In this case, a step will be generated near the boundary between the cap layer 44 and the intermediate layer 46, which may impair the appearance of the tire 2. From the viewpoint of maintaining a good appearance, it is preferable that the LAT wear index LATc of the cap layer 44 and the LAT wear index LATm of the intermediate layer 46 are approximately the same. Specifically, the difference (LATc-LATm) between the LAT wear index LATc of the cap layer 44 and the LAT wear index LATm of the intermediate layer 46 is preferably -10 or more and 10 or less. It is more preferable that this difference (LATc-LATm) is -5 or more and 5 or less. It is even more preferable that this difference (LATc-LATm) is 0.

[0116] Fig. 7 shows a portion of a tire 72 according to another embodiment of the present invention. Fig. 7 shows a meridian cross section of the tire 72. In Fig. 7, the left-right direction is the axial direction of the tire 72, and the up-down direction is the radial direction of the tire 72. The direction perpendicular to the paper surface of Fig. 7 is the circumferential direction of the tire 72.

[0117] This tire 72 has a configuration similar to that of the tire 2 shown in Fig. 1, except that the arrangement of the terminal portions 64 of the tire 2 shown in Fig. 1 is different. Therefore, in Fig. 7, the same components as those of the tire 2 in Fig. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

[0118] The tread 4 of this tire 72 is also composed of a first tread 50 and a second tread 52, similar to the tread 4 of the tire 2 shown in Fig. 1. In the tire 2 shown in Fig. 1, the terminal portion 64 is provided on the second tread 52, whereas in this tire 72, the terminal portion 64 is provided on the first tread 50. As shown in Fig. 7, the terminal portion 64 penetrates the intermediate layer 56 and the first inner layer 58. The terminal portion 64 is connected to the first outer layer 54 at its outer end. The terminal portion 64 is connected to the band 16 at its inner end.

[0119] As described above, the first outer layer 54 is made of the cap layer 44. Although not described in detail, from the viewpoint of exerting a high grip force, the reinforcing agent of the rubber composition for the cap layer 44 is mainly composed of carbon black. Therefore, the cap layer 44 has electrical conductivity. In other words, the cap layer 44 is made of a conductive rubber. Since the first outer layer 54 and the band 16 are connected by the terminal portion 64, electrical conductivity is ensured in this tire 72 as in the tire 2 shown in FIG. 1. Since the outer end of the terminal portion 64 is covered by the first outer layer 54, the terminal portion 64 of this tire 72 is not exposed on the tread surface T. Therefore, until the first outer layer 54 is worn away and disappears, the deterioration of the appearance quality of the tread 4 due to the terminal portion 64 is suppressed. Even if the tread 4 wears, the appearance state is maintained well. Even if the tread 4 wears, a stable ground contact shape is obtained, so that the tread 4 can fully exert its function. This tire 72 can achieve a reduction in rolling resistance while preventing a deterioration in appearance quality and a significant deterioration in wet performance due to wear.

[0120] As described above, according to the present invention, a tire can be obtained that can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear. EXAMPLES

[0121] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0122] [Example 1] A pneumatic tire for passenger cars (tire size=235 / 55R19) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below was obtained. A tread having a configuration shown in FIG. 1 was used, including a cap layer, a base layer, and an intermediate layer. The loss tangent LTc of the cap layer at 30° C. was 0.25. The loss tangent LTm of the intermediate layer at 30° C. was 0.15. The ratio of the loss tangent LTm to the loss tangent LTc (LTm / LTc) was 0.60. The loss tangent LTb of the base layer at 30° C. was 0.10. In the first tread, the ratio (TG / TC) of the thickness TG of the first outer layer to the total thickness TC of the thickness TG of the first outer layer and the thickness TK of the intermediate layer was 0.60. The ratio (TC / DG) of the total thickness TC to the groove depth DG of the circumferential groove was 0.95. A shoulder circumferential groove was formed in the first tread, and the ratio (WT1 / WH) of the axial distance WT1 from the reference ground contact edge PH on the first end TE1 side to the boundary PB to the contact width WH of the reference ground contact surface was 65%. The ratio (L1 / L2) of the first standard contact length L1 to the second standard contact length L2 was 0.75. The radius Rc of the center contour line was 700 mm. The terminal portion was provided on the second tread.

[0123] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that a tread having the configuration shown in Fig. 8 was used. The tread of Comparative Example 1 includes a cap layer, an intermediate layer, and a base layer. A first tread was constructed in which the cap layer was laminated on the base layer at the first end TE1 side, and a second tread was constructed in which the intermediate layer was laminated on the base layer at the second end TE2 side. The materials of the cap layer and the base layer are the same as those of the cap layer and the base layer in Example 1. By changing the rubber material, the loss tangent LTm of the intermediate layer was changed, and the ratio (LTm / LTc) was set as shown in Table 1 below. The ratio (WT1 / WH) of the axial distance WT1 from the reference ground edge PH on the first end TE1 side to the boundary PB to the ground contact width WH of the reference ground contact surface was 30%. The ratio (L1 / L2) of the first standard contact length L1 to the second standard contact length L2 was 0.50. The radius Rc of the center contour was 450 mm. The ratio of the thickness of the cap layer to the effective groove depth of the circumferential groove was 0.95. The ratio of the thickness of the intermediate layer to the effective groove depth of the circumferential groove was 0.95.

[0124] [Comparative Example 2] A tire of Comparative Example 2 was obtained in the same manner as Example 1, except that a tread having the configuration shown in Fig. 9 was used. The tread of Comparative Example 2 includes a cap layer, an intermediate layer, and a base layer. The materials of the cap layer, intermediate layer, and base layer are the same as those of the cap layer, intermediate layer, and base layer of Comparative Example 1. In this Comparative Example 2, a cap layer, an intermediate layer, and a base layer were laminated in the radial direction, and the entire tread was constituted by a laminate of these three layers. The ratio of the thickness of the cap layer to the total thickness of the cap layer and the intermediate layer was 0.75, as shown in the "TG / TC" column in Table 1 below. The ratio of the total thickness of the cap layer and the intermediate layer to the effective groove depth of the circumferential groove was 0.95. The ratio (L1 / L2) of the first standard contact length L1 to the second standard contact length L2 was 0.50. The radius Rc of the center contour was 450 mm.

[0125] [Comparative Example 3-4] A tire of Comparative Example 3-4 was obtained in the same manner as in Example 1, except that the ratio (TG / TC) was set as shown in Table 1 below.

[0126] [Example 2-3] Tires of Examples 2-3 were obtained in the same manner as in Example 1, except that the radius Rc and the ratio (L1 / L2) were as shown in Table 2 below.

[0127] [Example 4] A tire of Example 4 was obtained in the same manner as in Example 1, except that the arrangement of the terminal portions was as shown in FIG.

[0128] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) was measured when the prototype tire was running on a drum at a speed of 80 km / h under the following conditions. The results are shown in Table 1 below as an index, with Comparative Example 1 being set at 100. The higher the value, the lower the rolling resistance of the tire. In this evaluation, if the index exceeds 100, it is determined that a reduction in rolling resistance has been achieved. Rim: 19 x 7.5J Internal pressure: 210kPa Vertical load: 6.47kN

[0129] [Wet performance of new tires (WET)] A new prototype tire was mounted on a rim (size = 19 x 7.5J) and air was filled to adjust the internal pressure of the tire to 230 kPa. 3 The test vehicle was made to make a steady turn on a test course with a wet road surface (water film thickness = 1.4 mm), and the limit speed was measured. The results are shown in the "WET (NEW)" column of Tables 1 and 2 below, as an index with Comparative Example 1 set at 100. The higher the value, the higher the limit speed and the better the wet performance of the tire.

[0130] [Changes in wet performance due to wear] A new prototype tire was mounted on a rim (size = 19 x 7.5J) and air was filled to adjust the internal pressure of the tire to 230 kPa. 3The tires were fitted to a passenger car (of the same class). The test vehicle was run on a test course with a dry asphalt road surface to wear down the tire tread. The tread was worn down until the groove depth of the circumferential groove reached 50% of the groove depth of a new tire. The test vehicle was then run on a test course with a wet road surface (water film thickness = 1.4 mm) to make a steady turn and measure the limit speed. The change in wet performance due to wear was evaluated based on the difference between the limit speed obtained when the tire was new and this limit speed. The results are shown in the "Performance Change" column in Tables 1 and 2 below, with Comparative Example 1 set to 100 as an index. The higher the value, the more the deterioration of wet performance due to wear is suppressed.

[0131] [Appearance of worn tires] A new prototype tire was mounted on a rim (size = 19 x 7.5J) and air was filled to adjust the internal pressure of the tire to 230 kPa. 3 The test vehicle was run on a test course with a dry asphalt road surface to wear down the tire tread. The tread was worn down until the groove depth of the circumferential grooves reached 50% of the groove depth of a new tire. The wear state of the tread was then visually confirmed. The results are shown as an index in the "Appearance" column in Tables 1 and 2 below. The larger the value, the better the wear appearance. This evaluation was performed for Example 1 and Example 4.

[0132] [Table 1]

[0133] [Table 2]

[0134] As shown in Table 1-2, it has been confirmed that the examples can achieve a reduction in rolling resistance while preventing a significant decrease in wet performance due to wear. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0135] The technology described above that can achieve a reduction in rolling resistance while preventing a significant decrease in wet performance due to wear can be applied to various tires. [Explanation of symbols]

[0136] 2. 72... Tires 4. Tread 6. Sidewall 24, 24s, 24m...Circumferential groove 26, 26s, 26m, 26c...Land 44 Cap layer 46. ​​Middle class 48...Base layer 50···First tread 52...Second tread 54...first outer layer 56...intervening layer 58...First inner layer 60...Second outer layer 62...Second inner layer 64...Terminal section

Claims

1. A tire having a tread that comes into contact with a road surface, The tread comprises a cap layer, an intermediate layer having a loss tangent at 30°C lower than the loss tangent at 30°C of the cap layer, and a base layer having a loss tangent at 30°C lower than the loss tangent at 30°C of the intermediate layer, an orientation of the tread relative to a vehicle is specified; Of both ends of the tread, an end disposed on an outer side in a width direction of the vehicle is a first end, and an end disposed on an inner side is a second end, The tread is composed of a first tread located on the first end side and a second tread located on the second end side, the first tread includes a first outer layer, an intermediate layer positioned radially inward of the first outer layer, and a first inner layer positioned radially inward of the intermediate layer, The second tread includes a second outer layer and a second inner layer located radially inside the second outer layer, the first outer layer comprises the cap layer, the intermediate layer and the second outer layer are composed of the intermediate layer, the first inner layer and the second inner layer are made of the base layer, In the first tread, a ratio of a thickness of the first outer layer to a total thickness of a thickness of the first outer layer and a thickness of the intermediate layer is 0.50 or more and 0.70 or less. tire.

2. At least three circumferential grooves are formed in the tread and are aligned in the axial direction; Among the at least three circumferential grooves, a circumferential groove located on an outer side in the axial direction is a shoulder circumferential groove, The shoulder circumferential groove is formed in the first tread.

2. The tire of claim 1.

3. a ratio of a loss tangent at 30° C. of the intermediate layer to a loss tangent at 30° C. of the cap layer is 0.50 or more and 0.70 or less; 3. A tire according to claim 1 or 2.

4. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, the camber angle of the tire is set to -1°, and a load of 70% of the standard load is applied to the tire as a vertical load. The tire is brought into contact with a flat road surface, and the contact surface obtained is the standard contact surface. The contact length measured at a position corresponding to 80% of the contact width of the standard contact surface is the standard contact length, The standard contact length on the first end side is a first standard contact length, and the standard contact length on the second end side is a second standard contact length, A ratio of the first standard contact length to the second standard contact length is 0.60 or more and 0.90 or less. A tire according to any one of claims 1 to 3.

5. In a meridian cross section of the tire in a state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and no load is applied to the tire, an outer surface of the tire comprises a tread surface and a pair of side surfaces continuous with ends of the tread surface, The contour of the tread surface includes a curved contour line that passes through the equator of the tire and is formed of a circular arc, The radius of the curved contour is 500 mm or more and 1000 mm or less. A tire according to any one of claims 1 to 4.

6. The first tread has a terminal portion penetrating the intermediate layer and the first inner layer, The terminal portion is conductive. A tire according to any one of claims 1 to 5.

Images