tire

Abstract

To provide a tire 2 that can attain reduction in rolling resistance, while preventing significant deterioration in wet performance due to abrasion.SOLUTION: A tread 4 of a tire 2 comprises: a cap layer 38 constituting a portion of an outer surface of the tire 2; a base layer 40 positioned inside the cap layer 38 in a radial direction; and an intermediate layer 42 positioned between the cap layer 38 and the base layer 40 in the radial direction. A loss tangent at 30°C of the intermediate layer 42 is lower than a loss tangent at 30°C of the cap layer 38, and a loss tangent at 30°C of the base layer 40 is lower than the loss tangent at 30°C of the intermediate layer 42. The tread 4 includes at least two three-layered body parts 44 constituted of the cap layer 38, the intermediate layers 42, and the base layer 40, and at least one two-layered body part 46 positioned between a first three-layered body part 44a and a second three-layered body part 44b and constituted of the cap layer 38 and the base layer 40.SELECTED DRAWING: Figure 4

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.

[0004] The tread wears as the tire is driven. When the cap layer wears away, the middle layer comes into contact with the road surface. The rubber used in the middle layer is designed to contribute to wet performance rather than rolling resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-210044 A Summary of the Invention [Problem to be solved by the invention]

[0006] 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.

[0007] 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]

[0008] A tire according to one aspect of the present invention includes a tread that comes into contact with a road surface. At least three circumferential grooves are formed in the tread. The tire is assembled on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and a load of 70% of the standard load is applied to the tire as a vertical load, and the tire is brought into contact with a flat road surface, resulting in a contact surface that is a reference contact surface. The tread includes a cap layer that constitutes a part of the outer surface of the tire, a base layer that is located radially inside the cap layer, and an intermediate layer that is located radially between the cap layer and the base layer. The loss tangent at 30°C of the intermediate layer is lower than the loss tangent at 30°C of the cap layer, and the loss tangent at 30°C of the base layer is lower than the loss tangent at 30°C of the intermediate layer. The tread includes at least two three-layer body parts that are composed of the cap layer, the intermediate layer, and the base layer, and at least one two-layer body part that is located between a first three-layer body part and a second three-layer body part and that is composed of the cap layer and the base layer.

[0009] Preferably, in the tire, the circumferential groove is cut in the two-layer body portion. A groove bottom and a groove wall of the circumferential groove are formed by the cap layer.

[0010] Preferably, in this tire, the ratio of the sum of the thicknesses of the cap layers constituting the groove walls at a position 50% of the groove depth of the circumferential groove to the contact width of the reference contact surface is 5% or more and 15% or less.

[0011] Preferably, in the tire, a ratio of a thickness of the cap layer at a groove bottom of the circumferential groove to a thickness of the two-layer portion is equal to or greater than 30% and equal to or less than 70%.

[0012] Preferably, in this tire, the outer surface of the tire includes a tread surface and a pair of side surfaces connected to the edge of the tread surface. In the meridian section of the tire, the contour of the tread surface includes a plurality of curved contours consisting of arcs having different radii. The contour of the outer surface of the tire includes, at the edge of the tread surface, a curved portion consisting of a curved contour line consisting of an arc having a smallest radius among the plurality of curved contour lines included in the contour of the tread surface and connected to the side surface, an inner adjacent contour line located axially inside the curved portion and tangent to the curved portion, and an outer adjacent contour line located axially outside the curved portion and tangent to the curved portion. The intersection of the tangent to the curved portion at the tangent point between the inner adjacent contour line and the curved portion and the tangent to the curved portion at the tangent point between the outer adjacent contour line and the curved portion is the tread reference edge, and the axial distance from one of the tread reference edges to the other tread reference edge is the tread width. The ratio of the axial width of the two-layer body portion to the tread width is 20% or more and 50% or less.

[0013] Preferably, in the tire, a ratio of a thickness of the cap layer to a total thickness of the cap layer and the intermediate layer in the three-layer body portion is 30% or more and 50% or less.

[0014] 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 40% or greater and 90% or less.

[0015] Preferably, in the tire, a difference between an LAT abrasion index of the cap layer and an LAT abrasion index of the intermediate layer is equal to or greater than -10 and equal to or less than 10.

[0016] Preferably, in the tire, a difference between an elongation at break of the cap layer and an elongation at break of the intermediate layer is equal to or greater than -20% and equal to or less than 20%. Effect of the Invention

[0017] 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]

[0018] [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 image diagram illustrating the contact width of the reference contact surface. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing the contour of a shoulder portion of the tire of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a portion of the tire of FIG. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing the configuration of the tread in the circumferential groove. [Figure 6] FIG. 6 is a cross-sectional view showing a portion of a tire according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0020] In this disclosure, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state.

[0021] 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 matching the distance between the left and right beads in the tire section obtained by cutting the tire along a plane including the rotation axis to the distance between the beads in the tire when mounted on a normal rim.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[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 ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions. Initial distortion = 10% Dynamic strain = 2% Frequency = 10Hz Deformation mode = tension In this measurement, the test specimen is sampled from a tire. If it is not possible to sample the test specimen from a tire, the test specimen 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 elongation at break of an element made of crosslinked rubber among the elements constituting a tire is measured using a tensile tester in an atmosphere at a temperature of 23° C. in accordance with the provisions of JIS K6251. The No. 3 dumbbell test piece used for the measurement is sampled from 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.

[0029] 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 is measured using a friction tester, such as an LAT tester (Laboratory Abration and Skid Tester) such as LAT100 (manufactured by VMI) in accordance with the provisions of JIS K6264-1 (LAT100 abrasion test). In this measurement, a rubber composition used to form the element to be measured is vulcanized and molded in a mold for the test piece at 170°C for 20 minutes to prepare a test piece. Using this test piece, the volume loss of this test piece (volume loss of the evaluation object) is measured under conditions of a load of 50N, a speed of 20km / h, and a slip angle of 5°. The volume loss of the reference rubber composition (reference volume loss) is also measured in the same manner. Using the volume loss of the evaluation object and the reference volume loss, the LAT abrasion index of the evaluation object element is obtained by the following formula. LAT wear index = (reference volume loss amount / evaluation target volume loss amount) x 100 The LAT abrasion index is the volume loss of the object to be evaluated, expressed as an index with the reference volume loss being 100. There is no particular limitation on the reference rubber composition. For example, when obtaining the LAT abrasion index of a tread component, a rubber composition for a cap layer of a conventional tread composed of two layers, a cap layer and a base layer, is used as the reference rubber composition.

[0030] 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.

[0031] 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 and decorations such as designs and letters engraved on the outer surface.

[0032] 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.

[0033] 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.

[0034] In Fig. 1, the length indicated by the symbol WA is the maximum width, i.e., the cross-sectional width (see JATMA, etc.), of the tire 2. 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 position where the tire 2 shows the maximum width (hereinafter, the maximum width position).

[0035] 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 cushions 18 , a pair of chafers 20 , and an inner liner 22 .

[0036] The outer surface of the tread 4 comes into contact with the road surface. Grooves 24 are cut into the tread 4. This forms a tread pattern.

[0037] In this tire 2, at least three circumferential grooves 26 extending continuously in the circumferential direction are cut into the tread 4. As a result, at least four land portions 28 arranged in parallel in the axial direction are formed in the tread 4. In the tire 2 shown in Fig. 1, four land portions 28 are formed by cutting the three circumferential grooves 26 into the tread 4. The circumferential grooves 26 form part of the grooves 24 that form the tread pattern.

[0038] In Fig. 1, the position indicated by the 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. As shown in Fig. 1, when a groove 24 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 24 does not exist.

[0039] Each sidewall 6 is continuous with an end of the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 extends from the end 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.

[0040] 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.

[0041] Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 30 and an apex 32. Although not shown, the core 30 includes a steel wire.

[0042] The apex 32 is located radially outward of the core 30. The apex 32 tapers outward. The apex 32 is made of crosslinked rubber having high rigidity.

[0043] 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.

[0044] The carcass 12 includes at least one carcass ply 34. From the viewpoint of weight reduction, the carcass 12 of the tire 2 is configured with one carcass ply 34.

[0045] The carcass ply 34 includes a ply body 34a and a pair of turned-up portions 34b. The ply body 34a spans between one core 30 and the other core 30. Each turned-up portion 34b is continuous with the ply body 34a and is turned up from the inside to the outside in the axial direction at each core 30. In this tire 2, an end of the turned-up portion 34b is located outside the maximum width position PW in the radial direction.

[0046] Although not shown, the carcass ply 34 includes a number of carcass cords arranged in parallel. These carcass cords are covered with a topping rubber. 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.

[0047] 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.

[0048] The belt 14 is composed of at least two layers 36 laminated in the radial direction. The belt 14 of the tire 2 is composed of two layers 36 laminated in the radial direction. Of the two layers 36, the layer 36 located on the inner side is the inner layer 36a, and the layer 36 located on the outer side is the outer layer 36b. As shown in FIG. 1, the inner layer 36a is wider than the outer layer 36b. The length from an end of the outer layer 36b to an end of the inner layer 36a is 3 mm or more and 10 mm or less.

[0049] Although not shown, each of the inner layer 36a and the outer layer 36b includes a number of belt cords arranged in parallel. These belt cords are covered with a topping rubber. Each belt cord is inclined with respect to the equator plane. The material of the belt cord is steel.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The cushions 18 are spaced apart from each other in the axial direction. The cushions 18 are located between the ends of the belt 14 and the band 16 and the ply body 34a of the carcass 12. The cushions 18 are made of crosslinked rubber having low stiffness.

[0054] Each chafer 20 is located radially inside the bead 10. The chafer 20 contacts the rim R. The chafer 20 of the tire 2 is made of a cloth and rubber impregnated into the cloth.

[0055] The inner liner 22 is positioned inside the carcass 12. The inner liner 22 constitutes the inner surface of the tire 2. The inner liner 22 is made of a crosslinked rubber having a low gas permeability coefficient. The inner liner 22 maintains the internal pressure of the tire 2.

[0056] 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.

[0057] 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 normal state set to 0°, and bringing the tire 2 into contact with a flat road surface. 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 that corresponds to the axial outer end of the reference contact patch is the above-mentioned position PH. In the tire 2, this position PH is the reference contact end.

[0058] An image of the reference contact surface is shown in Figure 2. In Figure 2, 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 direction perpendicular to the paper surface of Figure 2 corresponds to the radial direction of the tire 2.

[0059] In Fig. 2, the length indicated by the symbol CW is the ground width of the reference ground plane. The ground width CW is the axial distance from one reference ground end PH to the other reference ground end PH. The ground width CW is represented by the maximum width of the reference ground plane.

[0060] Fig. 3 shows a part of the tire 2 shown in Fig. 1. In Fig. 3, 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. 3 is the circumferential direction of the tire 2.

[0061] Fig. 3 shows the contour of the shoulder portion of the tire 2 in a meridian cross section. The contour shown in Fig. 3 is obtained by measuring the outer surface shape of the tire 2 in a normal state with a displacement sensor.

[0062] 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.

[0063] 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, at the end portion of the tread surface T, a curved portion that 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. In FIG. 3, this curved portion is indicated by the symbol RS.

[0064] 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.

[0065] In Fig. 3, 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.

[0066] 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 edge PT to the other tread reference edge PT. In this tire 2, the ratio (WT / WA) of the tread width WT to the cross-sectional width WA is 70% or more and 90% or less. The ratio (CW / WT) of the aforementioned contact width CW of the reference contact surface to the tread width WT is 70% or more and 90% or less.

[0067] As described above, three circumferential grooves 26 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 three circumferential grooves 26 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.

[0068] In the tire 2, the circumferential groove 26 located on the outer side in the axial direction among the three circumferential grooves 26 is a shoulder circumferential groove 26s. The circumferential groove 26 located on the inner side of the shoulder circumferential groove 26s is a middle circumferential groove 26m.

[0069] As described above, the tread 4 of the tire 2 is configured with four land portions 28. Of the four land portions 28, the land portion 28 located on the equatorial plane side is the middle land portion 28m, and the land portion 28 located on the outer side of the middle land portion 28m is the shoulder land portion 28s. In the tire 2, of the land portions 28 configured in the tread 4, the land portion 28 located on the outer side in the axial direction is the shoulder land portion 28s.

[0070] The shoulder land portion 28s includes a reference ground contact edge PH. Between the left and right middle land portions 28m is a middle circumferential groove 26m. In the tire 2, the middle circumferential groove 26m is located on the equatorial plane. The middle circumferential groove 26m is also referred to as a center circumferential groove.

[0071] Fig. 4 shows a part of the tire 2 shown in Fig. 1. Fig. 4 shows a tread portion of the tire 2. In Fig. 4, 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. 4 is the circumferential direction of the tire 2.

[0072] The tread 4 of the tire 2 includes a cap layer 38, a base layer 40, and an intermediate layer 42. The cap layer 38 constitutes a part of the tire outer surface TS. The base layer 40 is located inside the cap layer 38 in the radial direction. The intermediate layer 42 is located between the cap layer 38 and the base layer 40 in the radial direction. In the tire 2, in the portion where the cap layer 38, the base layer 40, and the intermediate layer 42 extend in the axial direction, the cap layer 38, the base layer 40, and the intermediate layer 42 are configured to have a substantially uniform thickness, except in the vicinity of the tread reference end PT. The thicknesses of the cap layer 38, the base layer 40, and the intermediate layer 42 are appropriately set in consideration of the wet performance and rolling resistance.

[0073] In this tire 2, the loss tangent LTm of the intermediate layer 42 at 30°C is lower than the loss tangent LTc of the cap layer 38 at 30°C. The loss tangent LTb of the base layer 40 at 30°C is lower than the loss tangent LTm of the intermediate layer 42 at 30°C. The cap layer 38, the base layer 40, and the intermediate layer 42 are each made of a crosslinked rubber having a different heat buildup property. The cap layer 38 is most susceptible to heat buildup, and the base layer 40 is least susceptible to heat buildup. The intermediate layer 42 has heat buildup property between that of the cap layer 38 and that of the base layer 40.

[0074] The cap layer 38 having a high loss tangent LTc exerts a high grip force, and thus contributes to improving wet performance. The base layer 40 having a low loss tangent LTb is less likely to generate heat, and thus contributes to reducing rolling resistance. The intermediate layer 42 having an intermediate loss tangent LTm between the loss tangent LTc and the loss tangent LTb contributes to improving wet performance by setting the loss tangent LTm to a loss tangent close to the loss tangent LTc. By setting the loss tangent LTm to a loss tangent close to the loss tangent LTb, the intermediate layer 42 contributes to reducing rolling resistance.

[0075] As shown in FIG. 4, the tread 4 of the tire 2 includes a three-layer body 44, which is a laminate of the cap layer 38, the intermediate layer 42, and the base layer 40, and a two-layer body 46, which is a laminate of the cap layer 38 and the base layer 40. The two-layer body 46 is located between a first three-layer body 44a located on one side of the tire 2 in the axial direction and a second three-layer body 44b located on the other side. The tread 4 includes at least two three-layer body parts 44, which are composed of the cap layer 38, the intermediate layer 42, and the base layer 40, and at least one two-layer body part 46, which is composed of the cap layer 38 and the base layer 40 and is located between the first three-layer body part 44a and the second three-layer body part 44b. The tread 4 of the tire 2 includes four three-layer body parts 44 and three two-layer body parts 46, and the three-layer body parts 44 and the two-layer body parts 46 are arranged alternately in the axial direction.

[0076] When the tire 2 is new, the cap layer 38 constituting the outer surface of the tread 4 comes into contact with the road surface. Since the cap layer 38 exerts a high grip force, the tire 2 can obtain good wet performance. Although the tread 4 wears due to running, the two-layer body portion 46 of the tread 4 does not include the intermediate layer 42. The two-layer body portion 46 is located between the two three-layer body portions 44 in the axial direction. In the axial direction, the cap layer 38 of the two-layer body portion 46 is located next to the intermediate layer 42 of the three-layer body portion 44. Even if the tread 4 wears to the extent that the intermediate layer 42 of the three-layer body portion 44 is exposed, the contact surface of the tire 2 includes the cap layer 38 of the two-layer body portion 46. In the tire 2, even if the intermediate layer 42 having a loss tangent LTm close to the loss tangent LTb of the base layer 40 is used, the cap layer 38 exerts a high grip force, so that a significant decrease in wet performance is prevented even if the tread 4 wears. Since the intermediate layer 42 contributes to reducing the rolling resistance, the tire 2 can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear.

[0077] The loss tangent LTc of the cap layer 38 at 30°C is preferably 0.15 or more. This is because the cap layer 38 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 38 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 38 will increase the temperature of the intermediate layer 42 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 38 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and even more preferably 0.27 or less.

[0078] As described above, in the tire 2, the loss tangent Ltm of the intermediate layer 42 at 30° C. is lower than the loss tangent LTc of the cap layer 38 at 30° C. Specifically, the ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 42 at 30° C. to the loss tangent LTc of the cap layer 38 at 30° C. is preferably 40% or more and 90% or less.

[0079] By setting the ratio (LTm / LTc) to 40% or greater, the intermediate layer 42 can ensure the necessary rigidity and effectively contribute to improving the wet performance. From this viewpoint, (LTm / LTc) is more preferably 50% or greater, and further preferably 60% or greater.

[0080] Setting the ratio (LTm / LTc) to 90% or less allows the intermediate layer 42 to effectively contribute to reducing rolling resistance. From this viewpoint, (LTm / LTc) is more preferably 80% or less, and further preferably 70% or less.

[0081] In the tire 2, from the viewpoint of the intermediate layer 42 effectively contributing to reducing rolling resistance, the loss tangent Ltm of the intermediate layer 42 at 30° C. is preferably 0.15 or less, more preferably 0.14 or less, and further preferably 0.13 or less. From the viewpoint of the intermediate layer 42 being able to ensure necessary rigidity and effectively contributing to improving wet performance, the loss tangent Ltm of the intermediate layer 42 at 30° C. is preferably 0.10 or more, and more preferably 0.11 or more.

[0082] As described above, in the tire 2, the loss tangent LTb of the base layer 40 at 30° C. is lower than the loss tangent LTm of the intermediate layer 42 at 30° C. Specifically, the loss tangent LTb of the base layer 40 at 30° C. is preferably 0.10 or less. This is because the base layer 40 effectively contributes to reducing rolling resistance. From this viewpoint, the loss tangent LTb is more preferably 0.09 or less. The smaller the loss tangent LTb of the base layer 40, the more preferable it is, and therefore no preferable lower limit is set.

[0083] As shown in FIG. 4, in this tire 2, the circumferential grooves 26 are formed in the two-layer body portion 46 formed in the tread 4. The circumferential grooves 26 may be formed in all of the two-layer body portions 46 formed in the tread 4, or the circumferential grooves 26 may be formed in a part of the two-layer body portions 46 formed in the tread 4. In this tire 2, the circumferential grooves 26 are not formed in the three-layer body portion 44. The three-layer body portion 44 is a main component of the land portion 28. The three-layer body portion 44 constitutes the land portion 28. As shown in FIG. 4, in this tire 2, the first three-layer body portion 44a is a main component of the middle land portion 28m, and the second three-layer body portion 44b is a main component of the shoulder land portion 28s.

[0084] 5 shows a schematic diagram of a two-layer body portion 46 in which the circumferential groove 26 is formed. The circumferential groove 26 includes a groove bottom 48 and a pair of groove walls 50. Each groove wall 50 connects the groove bottom 48 to an edge 52 of the circumferential groove 26. The edge 52 of the circumferential groove 26 is a boundary between the circumferential groove 26 and the outer surface of the tread 4.

[0085] As shown in FIG. 5 , the groove bottom 48 and groove wall 50 of the circumferential groove 26 are formed by the cap layer 38. In other words, the entire circumferential groove 26 is formed by the cap layer 38. Since the circumferential groove 26 does not include, for example, an interface between the cap layer 38 and the intermediate layer 42, the occurrence of cracks originating from this interface, which has been observed in conventional tires, is prevented. Even if a crack occurs in the circumferential groove 26 due to a force acting on the circumferential groove 26, the growth of the crack is suppressed. In the tire 2, the occurrence of cracks in the circumferential groove 26 is prevented. In the tire 2, the circumferential groove 26 has excellent crack growth resistance.

[0086] In this tire 2, the edge 52 of the circumferential groove 26 is formed by the cap layer 38. Because the groove wall 50 of the circumferential groove 26 is formed by the cap layer 38, even if the tread 4 wears, the edge 52 of the circumferential groove 26 is formed by the cap layer 38. Because the cap layer 38 is made of a crosslinked rubber that takes into consideration contact with the road surface, even if the tread 4 wears, the intermediate layer 42 does not form the edge 52 of the circumferential groove 26, so chipping is unlikely to occur at the edge 52 of the circumferential groove 26. This tire 2 also has excellent chipping resistance.

[0087] The tire 2 can achieve a reduction in rolling resistance while preventing a significant decrease in wet performance due to wear, and is also excellent in crack growth resistance and chipping resistance.

[0088] In Fig. 5, the position indicated by the symbol PD is the position where the groove depth of the circumferential groove 26 is half. The length indicated by the symbol a is the thickness of the cap layer 38 constituting the groove wall 50 at the position PD where the groove depth of the circumferential groove 26 is 50%. In this tire 2, the portion of the cap layer 38 constituting the groove wall 50 that forms the interface with the intermediate layer 42 has a uniform thickness a. The length indicated by the symbol B is the thickness of the two-layer portion 46 at the groove bottom 48 of the circumferential groove 26. The length indicated by the symbol b is the thickness of the cap layer 38 at the groove bottom 48 of the circumferential groove 26.

[0089] In this tire 2, when the sum of the thicknesses a of the cap layers 38 constituting the groove walls 50 at the position PD that is 50% of the groove depth of the circumferential groove 26 is defined as A, the ratio (A / CW) of this sum A to the contact width CW of the reference contact surface is preferably 5% or more and 15% or less. In this tire 2, three two-layered portions 46 are formed in the tread 4, and the circumferential groove 26 is cut in each of the two-layered portions 46, so that the sum of the thicknesses a of the cap layers 38 in the six groove walls is used as the above-mentioned sum A.

[0090] By setting the ratio (A / CW) to 5% or more, the cap layer 38 included in the ground contact surface in a worn state effectively contributes to improving wet performance. From this viewpoint, the ratio (A / CW) is more preferably 7% or more, and further preferably 9% or more.

[0091] Setting the ratio (A / CW) to 15% or less suppresses the effect on rolling resistance of the cap layer 38. From this viewpoint, the ratio (A / CW) is more preferably 13% or less, and further preferably 11% or less.

[0092] In the tire 2, the ratio (b / B) of the thickness b of the cap layer 38 to the thickness B of the two-layer portion 46 at the groove bottom 48 of the circumferential groove 26 is preferably 30% or more and 70% or less.

[0093] Setting the ratio (b / B) to 30% or greater ensures the necessary thickness b of the cap layer 38 at the groove bottom 48. In the tire 2, even if a crack occurs at the groove bottom 48 of the circumferential groove 26 due to a force acting on the circumferential groove 26, growth of the crack is suppressed. The tire 2 has excellent crack growth resistance of the circumferential groove 26. From this viewpoint, the ratio (b / B) is more preferably 40% or greater, and further preferably 45% or greater.

[0094] Setting the ratio (b / B) to 70% or less suppresses the effect on rolling resistance of the cap layer 38. From this viewpoint, the ratio (b / B) is more preferably 60% or less, and further preferably 55% or less.

[0095] In this tire 2, the cap layer 38 and the intermediate layer 42 coexist in the three-layer body portion 44, which is the main component of the land portion 28. If there is a discrepancy between the wear resistance of the cap layer 38 and the wear resistance of the intermediate layer 42, 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 38 and the intermediate layer 42, 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 38 and the LAT wear index LATm of the intermediate layer 42 are approximately the same. Specifically, the difference (LATc-LATm) between the LAT wear index LATc of the cap layer 38 and the LAT wear index LATm of the intermediate layer 42 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.

[0096] As described above, the cap layer 38 and the intermediate layer 42 coexist in the three-layer body 44 of the tire 2. If there is a discrepancy between the elongation at break Ec of the cap layer 38 and the elongation at break Em of the intermediate layer 42, there is a concern that cracks may easily occur at the interface between the cap layer 38 and the intermediate layer 42. In this case, the land portion 28 may be easily chipped, and chipping resistance may be impaired. From the viewpoint of maintaining good chipping resistance, the difference (Ec-Em) between the elongation at break Ec of the cap layer 38 and the elongation at break Em of the intermediate layer 42 is preferably -20% or more and 20% or less. This difference (Ec-Em) is more preferably -10% or more and 10% or less, even more preferably -5% or more and 5% or less, and particularly preferably 0%.

[0097] As described above, in the tire 2, the main component of the shoulder land portion 28s is the three-layer body portion 44b. The shoulder land portion 28s includes the intermediate layer 42 that is less susceptible to heat generation than the cap layer 38. The shoulder land portion 28s contributes to reducing rolling resistance more than a shoulder land portion constituted by the cap layer 38 and the base layer 40.

[0098] In this tire 2, the ends of the band 16 and the belt 14 are covered with the base layer 40, and the ends of this base layer 40 are covered with the intermediate layer 42. At the ends of the tread 4, the intermediate layer 42 is located between the outer surface of the tire 2 and the base layer 40. At the ends of the tread 4, the base layer 40 is disposed at a position away from the outer surface of the tire 2. In this tire 2, exposure of the base layer 40 is prevented during cornering (hereinafter also referred to as severe cornering) in which a large inertial force is generated such that the ends of the tread 4 are worn down. This tire 2 also has excellent durability during severe cornering.

[0099] Fig. 6 shows a portion of a tire 62 according to another embodiment of the present invention. Fig. 6 shows a meridian cross section of the tire 62. In Fig. 6, the left-right direction is the axial direction of the tire 62, and the up-down direction is the radial direction of the tire 62. The direction perpendicular to the paper surface of Fig. 6 is the circumferential direction of the tire 62.

[0100] This tire 62 has a configuration similar to that of the tire 2 shown in Fig. 1, except for the tread 64. Therefore, in Fig. 6, 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.

[0101] The tread 64 of this tire 62 also includes a cap layer 66, a base layer 68, and an intermediate layer 70, similar to the tread 4 of the tire 2 shown in FIG. 1. The cap layer 66 constitutes a part of the tire outer surface TS. The base layer 68 is located inside the cap layer 66 in the radial direction. The intermediate layer 70 is located between the cap layer 66 and the base layer 68 in the radial direction. In the portion where the cap layer 66, the base layer 68, and the intermediate layer 72 extend in the axial direction, the cap layer 66, the base layer 68, and the intermediate layer 72 are configured to have a substantially uniform thickness, except in the vicinity of the tread reference end PT.

[0102] In this tire 62, the cap layer 66 is made of a crosslinked rubber similar to the cap layer 38 of the tire 2 shown in FIG. 1. The base layer 68 is made of a crosslinked rubber similar to the base layer 40 of the tire 2 shown in FIG. 1. The intermediate layer 70 is made of a crosslinked rubber similar to the intermediate layer 42 of the tire 2 shown in FIG. 1. Therefore, the loss tangent LTm of the intermediate layer 70 at 30° C. is lower than the loss tangent LTc of the cap layer 66 at 30° C. The loss tangent LTb of the base layer 68 at 30° C. is lower than the loss tangent LTm of the intermediate layer 70 at 30° C.

[0103] The concept of heat generation in the tread 64 in the tire 62 based on the loss tangents of the cap layer 66, the base layer 68, and the intermediate layer 70 is the same as the concept of heat generation in the tread 4 based on the loss tangents of the cap layer 38, the base layer 40, and the intermediate layer 42 in the tire 2 shown in FIG. 1. In other words, from the viewpoint of the cap layer 66 being able to contribute to the improvement of wet performance, the loss tangent LTc of the cap layer 66 at 30°C is preferably 0.15 or more. From the viewpoint of keeping the temperature state of the entire tread 64 stable and maintaining low rolling resistance, the loss tangent LTc of the cap layer 66 at 30°C is preferably 0.30 or less. The ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 70 at 30°C to the loss tangent LTc of the cap layer 66 at 30°C is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more, from the viewpoint of the intermediate layer 70 being able to ensure the necessary rigidity and effectively contribute to the improvement of wet performance. From the viewpoint of effectively contributing to the reduction of rolling resistance of the intermediate layer 70, this ratio (LTm / LTc) is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. From the viewpoint of effectively contributing to the reduction of rolling resistance of the base layer 68, the loss tangent LTb of the base layer 68 at 30°C is lower than the loss tangent LTm of the intermediate layer 70 at 30°C, specifically, is preferably 0.10 or less.

[0104] As shown in FIG. 6, the tread 64 of the tire 62 also includes a three-layer body 72, which is a laminate of the cap layer 66, the intermediate layer 70, and the base layer 68, and a two-layer body 74, which is a laminate of the cap layer 66 and the base layer 68. The two-layer body 74 is located between a first three-layer body 72a located on one side of the tire 62 in the axial direction and a second three-layer body 72b located on the other side. The tread 64 includes at least two three-layer body parts 72, which are composed of the cap layer 66, the intermediate layer 70, and the base layer 68, and at least a two-layer body part 74, which is located between the first three-layer body part 72a and the second three-layer body part 72b and is composed of the cap layer 66 and the base layer 68. The tread 64 of the tire 62 includes two three-layer body parts 72 and one two-layer body part 74, and the three-layer body parts 44 and the two-layer body parts 46 are arranged alternately in the axial direction.

[0105] When the tire 62 is new, the cap layer 66 constituting the outer surface of the tread 64 comes into contact with the road surface. Since the cap layer 66 exerts a high grip force, the tire 62 has good wet performance. The tread 64 wears down as the tire is driven, but the two-layer body portion 74 of the tread 64 does not include the intermediate layer 70. The two-layer body portion 74 is located between the two three-layer body portions 72 in the axial direction. In the axial direction, the cap layer 66 of the two-layer body portion 74 is located next to the intermediate layer 70 of the three-layer body portion 72. Even if the tread 64 wears down to the point where the intermediate layer 70 of the three-layer body portion 72 is exposed, the contact surface of the tire 62 includes the cap layer 66 of the two-layer body portion 74. In the tire 62, even if an intermediate layer 70 having a loss tangent LTm close to the loss tangent LTb of the base layer 68 is used, the cap layer 66 exerts a high grip force, so that a significant decrease in wet performance is prevented even if the tread 64 wears down. Since the intermediate layer 70 contributes to reducing the rolling resistance, the tire 62 can achieve reduced rolling resistance while preventing a significant decrease in wet performance due to wear.

[0106] 6, the length indicated by the symbol WD is the axial width of the two-layered portion 74. This axial width WD is represented by the axial distance between the interface between the cap layer 66 and the intermediate layer 70, which extend in a substantially radial direction, at the boundary between the three-layered portion 72 and the two-layered portion 74. When this axial distance varies in the radial direction, the axial width WD of the two-layered portion 74 is represented by the average value of the maximum distance and the minimum distance.

[0107] In the tire 62, the ratio (WD / WT) of the axial width WD of the double-layer portion 74 to the tread width WT is preferably 20% or more and 50% or less.

[0108] By setting the ratio (WD / WT) to 20% or more, the cap layer 66 included in the contact surface in a worn state effectively contributes to improving wet performance. From this viewpoint, the ratio (WD / WT) is more preferably 25% or more, and further preferably 30% or more.

[0109] Setting the ratio (WD / WT) to 50% or less suppresses the effect on rolling resistance of the cap layer 66. From this viewpoint, the ratio (WD / WT) is more preferably 45% or less, and further preferably 40% or less.

[0110] In FIG. 6, the symbol PQ is the width center of the three-layer body portion 72. In this tire 2, the width of the three-layer body portion 72 is represented by the axial distance from the interface between the cap layer 66 and the intermediate layer 70, which is the reference position for measuring the axial width WD, to the tread end PT. The length indicated by the symbol tc is Width center PQ The length indicated by the symbol t is the thickness of the cap layer 66 at this Width center PQ and the thickness tm of the intermediate layer 70. In this tire 2, the thickness tc is the thickness of the cap layer 66 at the three-layer body portion 72, and the total t is the sum of the thickness tc of the cap layer 66 at the three-layer body portion 72 and the thickness tm of the intermediate layer 70.

[0111] In the tire 2, in the three-layer body 72, the ratio (tc / t) of the thickness tc of the cap layer 66 to the sum t of the thickness tc of the cap layer 66 and the thickness tm of the intermediate layer 70 is preferably 30% or more and 50% or less.

[0112] By setting the ratio (tc / t) to be equal to or greater than 30%, the cap layer 66 effectively contributes to improving the wet performance. From this viewpoint, the ratio (tc / t) is more preferably equal to or greater than 35%.

[0113] Setting the ratio (tc / t) to 50% or less suppresses the effect of the cap layer 66 on the rolling resistance. From this viewpoint, the ratio (tc / t) is more preferably 45% or less.

[0114] 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

[0115] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0116] [Study 1] [Example 1] A pneumatic tire for passenger cars (tire size=205 / 55R16) 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. 4 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 60%. The loss tangent LTb of the base layer at 30° C. was 0.10. In this Example 1, the ratio (A / CW) of the sum A of the thicknesses a of the cap layers constituting the groove walls to the contact width CW of the reference contact surface at the position of 50% of the groove depth of the circumferential groove was 10%. The ratio (b / B) of the thickness b of the cap layer to the thickness B of the two-layer body portion at the groove bottom of the circumferential groove was 50%. In this Example 1, the difference (Ec-Em) between the elongation at break Ec of the cap layer and the elongation at break Em of the intermediate layer was 0%. The difference (LATc-LATm) between the LAT abrasion index of the cap layer and the LAT abrasion index of the intermediate layer was 0. The LAT abrasion index was measured using the rubber composition for the cap layer of Comparative Example 1 as the standard rubber composition.

[0117] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that in the radial direction, an intermediate layer was laminated on a base layer, a cap layer was laminated on the intermediate layer, and the loss tangent LTm of the intermediate layer was changed by changing the rubber material to set the ratio (LTm / LTc) as shown in Table 1 below. A two-layer body portion was not formed in the tread of Comparative Example 1. The groove wall of the circumferential groove includes an interface between the cap layer and the intermediate layer, and an interface between the intermediate layer and the base layer. In this Comparative Example 1, the difference (Ec-Em) between the elongation at break Ec of the cap layer and the elongation at break Em of the intermediate layer was 0%. The difference (LATc-LATm) between the LAT wear index of the cap layer and the LAT wear index of the intermediate layer was 0.

[0118] [Example 2-3] Tires of Examples 2-3 were obtained in the same manner as in Example 1, except that the thickness a of the cap layer constituting the groove wall of the circumferential groove was changed to set the ratio (A / CW) as shown in Table 1 below.

[0119] [Example 4-5] Tires of Examples 4-5 were obtained in the same manner as in Example 1, except that the thickness b of the cap layer at the groove bottom of the circumferential groove was changed to make the ratio (b / B) as shown in Table 1 below.

[0120] [Example 6] A tire of Example 6 was obtained in the same manner as Example 1, except that the loss tangent LTm of the intermediate layer was changed by changing the rubber material so that the ratio (LTm / LTc) was as shown in Table 1 below. In this Example 6, the difference (Ec-Em) between the elongation at break Ec of the cap layer and the elongation at break Em of the intermediate layer was 0%. The difference (LATc-LATm) between the LAT wear index of the cap layer and the LAT wear index of the intermediate layer was 0.

[0121] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) of the prototype tire was measured when it was running on a drum at a speed of 80km / h under the following conditions. The results are shown as an index in Table 1 below. The higher the value, the lower the rolling resistance of the tire. Rim: 16×6.5J Internal pressure: 210kPa Vertical load: 4.82kN

[0122] [Wet performance of worn tires (WET)] A new prototype tire was mounted on a rim (size = 16 x 7J) and air was filled to adjust the tire's internal pressure to 250 kPa. The tire was mounted on a test vehicle (passenger car). The test vehicle was driven 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 test vehicle was then driven on a test course with a wet road surface (water film thickness = 1.4 mm). The test vehicle was braked while traveling at a speed of 100 km / h, and the distance traveled from braking to stopping (braking distance) was measured. The results are shown as an index in Table 1 below. The higher the value, the shorter the braking distance and the better the tire's wet performance.

[0123] [Chipping resistance of worn tires (chipping)] A new prototype tire was mounted on a rim (size = 16 x 7J) and air was filled to adjust the internal pressure of the tire to 250 kPa. The tire was mounted on a test vehicle (passenger car). 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 test vehicle was then run on a test course with an unpaved road surface that included rubble. After running 3000 km, the appearance of the tread was visually observed and the occurrence of chipping (size and number of chips) was confirmed. The results are shown as an index in Table 1 below. The higher the value, the more chipping is suppressed and the better the tire's chipping resistance performance.

[0124] [Overall performance] The sum of the scores obtained in each evaluation was calculated. The results are shown in the "Overall" column in Table 1 below. The higher the score, the more preferable it is.

[0125] [Table 1]

[0126] [Consideration 2] [Example 7] A tire of Example 7 was obtained in the same manner as in Example 1, except that the tire tread configuration was as shown in Figure 6. The rubbers of the cap layer, intermediate layer and base layer of Example 7 were the same as those of the cap layer, intermediate layer and base layer of Example 1. In Example 7, the ratio (WD / WT) of the axial width WD of the two-layer body to the tread width WT was 30%. In the three-layer body, the ratio (tc / t) of the thickness tc of the cap layer to the sum t of the thickness tc of the cap layer and the thickness tm of the intermediate layer was 30%.

[0127] [Comparative Example 2] Except for forming the intermediate layer from the same rubber as the cap layer, a tire of Comparative Example 2 was obtained in the same manner as in Example 7. In the tread of Comparative Example 2, no two-layer portion was formed.

[0128] [Comparative Example 3] A tire of Comparative Example 3 was obtained in the same manner as in Example 7, except that in the radial direction, the intermediate layer was laminated on the base layer, and the cap layer was laminated on the intermediate layer. In the tread of Comparative Example 3, no two-layer portion was formed.

[0129] [Example 8] A tire of Example 8 was obtained in the same manner as in Example 7, except that the thickness tc of the cap layer in the three-layer body was changed to give the ratio (tc / t) as shown in Table 2 below.

[0130] [Example 9] A tire of Example 9 was obtained in the same manner as in Example 7, except that the width WD of the double-layer portion was changed to make the ratio (WD / WT) as shown in Table 2 below.

[0131] [Example 10] A tire of Example 10 was obtained in the same manner as in Example 7, except that the loss tangent LTm of the intermediate layer was changed by changing the rubber material so that the ratio (LTm / LTc) was as shown in Table 2 below. In this Example 10, the difference (Ec-Em) between the elongation at break Ec of the cap layer and the elongation at break Em of the intermediate layer was 0%. The difference (LATc-LATm) between the LAT wear index of the cap layer and the LAT wear index of the intermediate layer was 0.

[0132] [Rolling resistance coefficient (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) of the prototype tire was measured when it was running on a drum at a speed of 80km / h under the following conditions. The results are shown as an index in Table 2 below. The smaller the value, the lower the rolling resistance of the tire. Rim: 16×6.5J Internal pressure: 210kPa Vertical load: 4.82kN

[0133] [Wet performance of new tires (WET)] A new prototype tire was mounted on a rim (size = 16 x 7.0J) and filled with air to adjust the tire's internal pressure to 250 kPa. The tire was mounted on a test vehicle (passenger car). The test vehicle was driven on a test course with a wet road surface (water film thickness = 1.4 mm). The test vehicle was traveling at a speed of 80 km / h when the brakes were applied, and the distance traveled from when the brakes were applied until the tire came to a stop (braking distance) was measured. The results are shown as an index in the "WET (NEW)" column in Table 2 below. The higher the value, the shorter the braking distance and the better the tire's wet performance.

[0134] [Wet performance of worn tires (WET)] A new prototype tire was mounted on a rim (size = 16 x 7.0J) and filled with air to adjust the internal tire pressure to 250 kPa. The tire was mounted on a test vehicle (passenger car). The test vehicle was run on a test course with a dry asphalt surface to wear down the tire. When the tread depth reached 70% of that of a new tire, the wet performance of the worn tire was evaluated in the same manner as the wet performance of a new tire described above. The results are shown as an index in the "WET (OLD)" column in Table 2 below. The higher the value, the shorter the braking distance and the better the tire's wet performance. In this evaluation, if the index is 55 or higher, the tire is acceptable as it maintains good wet performance.

[0135] [Overall performance] The sum of the indices obtained in each evaluation was calculated. The results are shown in the "Overall" column in Table 2 below. The higher the value, the more preferable it is.

[0136] [Table 2]

[0137] 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]

[0138] 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]

[0139] 2. 62... Tires 4, 64... tread 6. Sidewall 12. Carcass 14. Belt 16...Band 26, 26s, 26m...Circumferential groove 28, 28s, 28m...Land 34, 34a, 34b... Carcass ply 36, 36a, 36b...layer 38, 66... ​​Cap layer 40, 68... Base layer 42, 70: Middle class 44, 44a, 44b, 72, 72a, 72b...three-layer body part 46, 74...Two-layer body part 48...groove bottom 50 Groove wall 52 Edge of circumferential groove 26

Claims

1. A tire having a tread that comes into contact with a road surface and at least three circumferential grooves cut into the tread, The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, 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 reference contact surface. The tread comprises a cap layer constituting a part of an outer surface of the tire, a base layer positioned radially inside the cap layer, and an intermediate layer positioned radially between the cap layer and the base layer, a loss tangent at 30° C. of the intermediate layer is lower than a loss tangent at 30° C. of the cap layer, and a loss tangent at 30° C. of the base layer is lower than a loss tangent at 30° C. of the intermediate layer; The tread includes at least two three-layer body portions each including the cap layer, the intermediate layer, and the base layer, and at least one two-layer body portion located between the first three-layer body portion and the second three-layer body portion and each including the cap layer and the base layer, a difference between the elongation at break of the cap layer and the elongation at break of the intermediate layer is −20% or more and 20% or less; tire.

2. The circumferential groove is formed in the two-layer body portion, A groove bottom and a groove wall of the circumferential groove are formed by the cap layer.

2. The tire of claim 1.

3. a ratio of a total thickness of the cap layer constituting the groove wall at a position of 50% of the groove depth of the circumferential groove to a contact width of the reference contact surface is 5% or more and 15% or less; 3. The tire of claim 2.

4. a ratio of a thickness of the cap layer at a groove bottom of the circumferential groove to a thickness of the two-layer portion is 30% or more and 70% or less; 4. A tire according to claim 2 or 3.

5. The outer surface of the tire includes a tread surface and a pair of side surfaces continuous with ends of the tread surface, In a meridian cross section of the tire, a profile of the tread surface includes a plurality of curved profile lines formed of arcs having different radii, a contour of an outer surface of the tire includes, at an end portion of the tread surface, a curved portion formed of a curved contour line connected to the side surface and consisting of an arc having a smallest radius among a plurality of curved contour lines included in the contour of the tread surface, an inner adjacent contour line located axially inside the curved portion and tangent to the curved portion, and an outer adjacent contour line located axially outside the curved portion and tangent to the curved portion, an intersection point between a tangent to the curved portion at a tangent point between the inner adjacent contour line and the curved portion and a tangent to the curved portion at a tangent point between the outer adjacent contour line and the curved portion is a tread reference edge; The axial distance from one tread reference end to the other tread reference end is the tread width, The ratio of the axial width of the two-layer body portion to the tread width is 20% or more and 50% or less.

2. The tire of claim 1.

6. In the three-layer body, the ratio of the thickness of the cap layer to the total thickness of the cap layer and the intermediate layer is 30% or more and 50% or less.

6. The tire of claim 5.

7. 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 40% or more and 90% or less; A tire according to any one of claims 1 to 6.

8. The difference between the LAT abrasion index of the cap layer and the LAT abrasion index of the intermediate layer is -10 or more and 10 or less. A tire according to any one of claims 1 to 7.

9. A tire having a tread that comes into contact with a road surface and at least three circumferential grooves cut into the tread, The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, 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 reference contact surface. The tread comprises a cap layer constituting a part of an outer surface of the tire, a base layer positioned radially inside the cap layer, and an intermediate layer positioned radially between the cap layer and the base layer, a loss tangent at 30° C. of the intermediate layer is lower than a loss tangent at 30° C. of the cap layer, and a loss tangent at 30° C. of the base layer is lower than a loss tangent at 30° C. of the intermediate layer; The tread includes at least two three-layer body portions each composed of the cap layer, the intermediate layer, and the base layer, and at least one two-layer body portion positioned between the first three-layer body portion and the second three-layer body portion and composed of the cap layer and the base layer, The circumferential groove is formed in the two-layer body portion, a groove bottom and a groove wall of the circumferential groove are formed by the cap layer, a ratio of a total thickness of the cap layer constituting the groove wall at a position that is 50% of the groove depth of the circumferential groove to a ground contact width of the reference ground contact surface is 5% or more and 15% or less; tire.

10. A tire having a tread that comes into contact with a road surface and at least three circumferential grooves cut into the tread, The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, 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 reference contact surface. The tread comprises a cap layer constituting a part of an outer surface of the tire, a base layer positioned radially inside the cap layer, and an intermediate layer positioned radially between the cap layer and the base layer, a loss tangent at 30° C. of the intermediate layer is lower than a loss tangent at 30° C. of the cap layer, and a loss tangent at 30° C. of the base layer is lower than a loss tangent at 30° C. of the intermediate layer; The tread includes at least two three-layer body portions each composed of the cap layer, the intermediate layer, and the base layer, and at least one two-layer body portion positioned between the first three-layer body portion and the second three-layer body portion and composed of the cap layer and the base layer, The outer surface of the tire includes a tread surface and a pair of side surfaces continuous with ends of the tread surface, In a meridian cross section of the tire, a profile of the tread surface includes a plurality of curved profile lines formed of arcs having different radii, a contour of an outer surface of the tire includes, at an end portion of the tread surface, a curved portion formed of a curved contour line connected to the side surface and consisting of an arc having a smallest radius among a plurality of curved contour lines included in the contour of the tread surface, an inner adjacent contour line located axially inside the curved portion and tangent to the curved portion, and an outer adjacent contour line located axially outside the curved portion and tangent to the curved portion, an intersection point between a tangent to the curved portion at a tangent point between the inner adjacent contour line and the curved portion and a tangent to the curved portion at a tangent point between the outer adjacent contour line and the curved portion is a tread reference edge; The axial distance from one tread reference end to the other tread reference end is the tread width, The ratio of the axial width of the two-layer body portion to the tread width is 20% or more and 50% or less. tire.

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