tire

Abstract

To provide a tire 2 that can attain reduction of rolling resistance while maintaining excellent wet performance and excellent durability.SOLUTION: A tread 4 of a tire 2 comprises a cap layer 38, an intermediate layer 40 whose loss tangent at 30°C is lower than a loss tangent at 30°C of the cap layer 38, and a base layer 42 whose loss tangent at 30°C is lower than the loss tangent at 30°C of the intermediate layer 40. In a radial direction, the intermediate layer 40 is positioned outside the base layer 42, and the cap layer 38 is positioned outside the intermediate layer 40. In an axial direction, an outer end PM of the intermediate layer 40 is positioned outside an outer end PB of the base layer 42, and an outer end PC of the cap layer 38 is positioned inside the outer end PM of the intermediate layer 40. A difference between a width WC in the axial direction of the cap layer 38 and a width WB in the axial direction of the base layer 42 is -10 mm or more and 10 mm or less.SELECTED DRAWING: Figure 3

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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-2008 A Summary of the Invention [Problem to be solved by the invention]

[0004] Considering the impact on the environment, there is a demand for further reduction in the rolling resistance of tires. As mentioned above, if the proportion of low heat generation rubber in the tread is increased in order to reduce rolling resistance, wet performance will decrease. Since low heat generation rubber is brittle, there is a concern that durability will decrease if the proportion of low heat generation rubber in the tread is increased. There is a demand for the establishment of technology that can achieve reduction in rolling resistance while maintaining good wet performance and good durability.

[0005] 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 maintaining good wet performance and good durability. [Means for solving the problem]

[0006] 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, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer. In the radial direction, the intermediate layer is located outside the base layer, and the cap layer is located outside the intermediate layer. In the axial direction, an outer end of the intermediate layer is located outside the outer end of the base layer, and an outer end of the cap layer is located inside the outer end of the intermediate layer. A difference between an axial width of the cap layer and an axial width of the base layer is -10 mm or more and 10 mm or less.

[0007] Preferably, in the tire, a difference in axial width between the intermediate layer and the cap layer is equal to or greater than 10 mm and equal to or less than 30 mm.

[0008] Preferably, in the tire, a difference between an axial width of the base layer and a width of the tread is equal to or greater than -10 mm and equal to or less than 10 mm.

[0009] Preferably, in this tire, the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and a load of 70% of the regular load is applied to the tire as a vertical load, and the tire is brought into contact with a flat road surface to obtain a contact surface, which is a reference contact surface, and a position on the outer surface of the tire that corresponds to the axial outer end of the reference contact surface is a reference contact edge. In the axial direction, the outer end of the cap layer is located outside the reference contact edge.

[0010] Preferably, in the tire, a ratio of a loss tangent at 30° C. of the cap layer to a loss tangent at 30° C. of the intermediate layer is 110% or greater and 250% or less.

[0011] Preferably, the tire comprises a belt located radially inside the tread, and a band located between the tread and the belt. The belt includes a number of parallel belt cords. The band includes a spirally wound band cord. The band is wider than the belt. In the axial direction, the position of an outer end of the base layer coincides with the position of an outer end of the band, or the outer end of the base layer is located outside the outer end of the band.

[0012] Preferably, in the tire, a ratio of an axial width of the cap layer to a section width of the tire is equal to or greater than 70% and equal to or less than 90%. Effect of the Invention

[0013] According to the present invention, it is possible to obtain a tire that can achieve reduced rolling resistance while maintaining good wet performance and good durability. [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 the tire of FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing a portion of the tire of FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a part of the tire of Comparative Example 1. As shown in FIG. [Diagram 5] FIG. 5 is an enlarged cross-sectional view showing a part of the tire of Comparative Example 2. As shown in FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a part of the tire of Comparative Example 3. As shown in FIG. [Figure 7] FIG. 7 is an enlarged cross-sectional view showing a part of the tire of Comparative Example 4. 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 appropriate reference to the drawings.

[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 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.

[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 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.

[0024] 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.

[0025] 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 patterns and letters engraved on the outer surface.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 .

[0030] 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.

[0031] At least three circumferential grooves 26 extending continuously in the circumferential direction are formed in the tread 4, and at least four land portions 28 arranged in parallel in the axial direction are formed. In the tire 2, as shown in FIG. 1, three circumferential grooves 26 are formed in the tread 4, and four land portions 28 are formed in the tread 4. The circumferential grooves 26 form part of the grooves 24 that form the tread pattern. 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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 10 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.

[0046] The cushions 18 are disposed at intervals 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 rigidity. In the tire 2, the cushions 18 may not be provided.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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. 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.

[0051] 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.

[0052] Fig. 2 shows the contour of a shoulder portion of a tire 2 in a meridian cross section. 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.

[0053] 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.

[0054] 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, a curved portion that is a curved contour line that is made of an arc having the smallest radius among the plurality of curved contour lines included in the contour of the tread surface and that connects to the side surface. In FIG. 2, this curved portion is indicated by the symbol RS.

[0055] 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.

[0056] 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 imaginary tread edge.

[0057] The portion of the tread 4 from one imaginary tread edge PT to the other imaginary tread edge PT is an area (hereinafter also referred to as a normal contact area) that is expected to come into contact with the road surface under normal driving conditions of the tire 2. From the viewpoint of effective reinforcement of the portion of the tread 4 (hereinafter also referred to as a tread portion), the belt 14 and band 16 described above are disposed in this normal contact area.

[0058] In Fig. 1, the length indicated by the double-headed arrow WT is the width of the tread 4. This width of the tread 4 is the axial distance from one imaginary tread edge PT to the other imaginary tread edge PT. The length indicated by the double-headed arrow WH is the axial width of the reference ground contact surface. The axial width WH is the axial distance from one reference ground contact edge PH to the other reference ground contact edge PH.

[0059] In this tire 2, the ratio (WT / WA) of the width WT of the tread 4 to the cross-sectional width WA is 70% or more and 90% or less. The virtual tread edge PT is located axially outboard of the reference ground contact edge PH. In other words, the axial width WH of the reference ground contact surface is narrower than the width WT of the tread 4. Specifically, the ratio (WH / WT) of the axial width WH to the width WT of the tread 4 is 70% or more and 90% or less.

[0060] Fig. 3 shows a part of the tire 2 shown in Fig. 1. Fig. 3 shows a tread portion of the tire 2. 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] The tread 4 of the tire 2 includes a cap layer 38, an intermediate layer 40, and a base layer 42. In the radial direction, the intermediate layer 40 is located outside the base layer 42, and the cap layer 38 is located outside the intermediate layer 40. As shown in FIG. 3 , the cap layer 38 is laminated on the intermediate layer 40, and the intermediate layer 40 is laminated on the base layer 42.

[0062] In the tire 2, the ratio of the thickness of the cap layer 38 to the thickness of the tread 4 at the width center of the land portion 28 is preferably 10% or more and 40% or less. At the width center of the land portion 28, the ratio of the thickness of the intermediate layer 40 to the thickness of the tread 4 is 30% or more and 70% or less.

[0063] In FIG. 3, the position indicated by the symbol PC is the outer end of the cap layer 38. The length indicated by the symbol WC is the axial width of the cap layer 38. The axial width WC is the axial distance from one outer end PC to the other outer end PC. The position indicated by the symbol PM is the outer end of the intermediate layer 40. The length indicated by the symbol WM is the axial width of the intermediate layer 40. The axial width WM is the axial distance from one outer end PM to the other outer end PM. The position indicated by the symbol PB is the outer end of the base layer 42. The length indicated by the symbol WB is the axial width of the base layer 42. The axial width WB is the axial distance from one outer end PB to the other outer end PB.

[0064] 3, the position indicated by the symbol PS is the outer end of the tread 4 on the tire outer surface TS. In this tire 2, the outer end PS of the tread 4 is located axially outboard of the outer end PC of the cap layer 38. Of the tire outer surface TS, a portion from the outer end PC to the outer end PS is formed by the intermediate layer 40. In this tire 2, a portion of the intermediate layer 40 is exposed to the tire outer surface TS.

[0065] The cap layer 38, the intermediate layer 40, and the base layer 42 are each made of crosslinked rubber having different heat generation properties. In this tire 2, the cap layer 38 is most susceptible to heat generation, and the base layer 42 is least susceptible to heat generation. The intermediate layer 40 has heat generation properties between the heat generation properties of the cap layer 38 and the base layer 42. In this tire 2, the loss tangent LTm of the intermediate layer 40 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 42 at 30°C is lower than the loss tangent LTm of the intermediate layer 40 at 30°C.

[0066] The loss tangent LTb of the base layer 42 at 30°C is preferably 0.11 or less. This is because the base layer 42 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. The smaller the loss tangent LTb of the base layer 42, the more preferable it is, and therefore no preferable lower limit is set.

[0067] The loss tangent Ltm of the intermediate layer 40 at 30°C is preferably 0.15 or less. This is because the intermediate layer 40 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 40 at 30°C is preferably 0.11 or more. This is because the intermediate layer 40 can ensure the necessary rigidity and effectively contribute to improving wet performance. From this viewpoint, the loss tangent LTm is more preferably 0.12 or more.

[0068] 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 40 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.

[0069] In this tire 2, an outer end PM of the intermediate layer 40 is located outside an outer end PB of the base layer 42 in the axial direction. The boundary between the intermediate layer 40 and the sidewall 6 bridges the tire outer surface TS and the outer surface of the carcass 12. This boundary is located outside the base layer 42 in the axial direction. In this tire 2, the intermediate layer 40 is located between the base layer 42 and the sidewall 6. The intermediate layer 40 covers the base layer 42 from the radial outer side and the axial outer side.

[0070] When a vehicle runs under harsh conditions that generate large inertial forces, wear occurs at the boundary portion (hereinafter also referred to as the buttress portion) between the tread 4 and the sidewall 6. In this tire 2, since the intermediate layer 40 having a sufficient thickness is located between the tire outer surface TS and the base layer 42, exposure of the base layer 42 is prevented even when this tire 2 is used under marginal running conditions that may cause wear at the buttress portion. In this tire 2, good durability is maintained.

[0071] In this tire 2, the outer end PC of the cap layer 38 is located inside the outer end PM of the intermediate layer 40 in the axial direction. In other words, the cap layer 38 covers not the entire intermediate layer 40 but part of the intermediate layer 40. In this tire 2, compared to a tread 4 in which the entire intermediate layer 40 is covered with the cap layer 38, the volume of the cap layer 38 that increases the rolling resistance is reduced, and the volume of the intermediate layer 40 that contributes to reducing the rolling resistance is increased. This tread 4 contributes to reducing rolling resistance.

[0072] In this tire 2, the difference (WC-WB) between the axial width WC of the cap layer 38 and the axial width WB of the base layer 42 is -10 mm or more and 10 mm or less. The axial width WC of the cap layer 38 and the axial width WB of the base layer 42 are approximately equal to each other. Since the heat generation and rigidity of the tread 4 as a whole are well balanced, the cap layer 38 can effectively contribute to improving wet performance, and the base layer 42 can effectively contribute to reducing rolling resistance. From this viewpoint, the difference (WC-WB) is preferably -5 mm or more and 5 mm or less.

[0073] In this tire 2, in the axial direction, an outer end PM of the intermediate layer 40 is located outside an outer end PB of the base layer 42, and an outer end PC of the cap layer 38 is located inside the outer end PM of the intermediate layer 40. A difference (WC-WB) between an axial width WC of the cap layer 38 and an axial width WB of the base layer 42 is -10 mm or more and 10 mm or less. This tire 2 can achieve reduced rolling resistance while maintaining good wet performance and good durability.

[0074] In the tire 2, the portion of the tread 4 consisting of the cap layer 38 and the intermediate layer 40 corresponds to the cap layer of the tread of a conventional tire consisting of the cap layer and the base layer. In the tire 2, from the viewpoint that the tread 4 can effectively contribute to improving the wet performance and reducing the rolling resistance, the ratio (Ltc / Ltm) of the loss tangent LTc of the cap layer 38 at 30°C to the loss tangent LTm of the intermediate layer 40 at 30°C is preferably 110% or more and 250% or less. This ratio (Ltc / Ltm) is more preferably 130% or more, and further preferably 150% or more. This ratio (Ltc / Ltm) is more preferably 240% or less, and further preferably 230% or less.

[0075] In the tire 2, from the viewpoint of allowing the cap layer 38 to effectively contribute to wet performance, the ratio (WC / WA) of the axial width WC of the cap layer 38 to the cross-sectional width WA of the tire 2 is preferably 70% or more, and more preferably 75% or more. From the viewpoint of effectively suppressing the effect of the cap layer 38 on rolling resistance, the ratio (WC / WA) is preferably 90% or less, and more preferably 85% or less.

[0076] In this tire 2, from the viewpoint of reducing rolling resistance, the difference (WM-WC) between the axial width WM of the intermediate layer 40 and the axial width WC of the cap layer 38 is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less. From the viewpoint of effectively contributing to preventing exposure of the base layer 42 during critical running, this difference (WM-WC) is preferably 10 mm or more. In this tire 2, from the viewpoint of effectively reducing rolling resistance while preventing exposure of the base layer 42, it is particularly preferable that this difference (WM-WC) is 10 mm.

[0077] In this tire 2, the difference (WB-WT) between the axial width WB of the base layer 42 and the width WT of the tread 4 is preferably -10 mm or more and 10 mm or less. In other words, it is preferable that the axial width WB of the base layer 42 is approximately equal to the width WT of the tread 4. This effectively ensures the axial width WB of the base layer 42 and the distance from the tire outer surface TS to the base layer 42. In this tire 2, exposure of the base layer 42 during critical running is effectively prevented, and the base layer 42 stably exhibits the rolling resistance reducing function. In this tire 2, good durability and low rolling resistance are obtained. From this viewpoint, the difference (WB-WT) is more preferably -5 mm or more, and more preferably 5 mm or less.

[0078] As described above, in the tire 2, the outer end PM of the intermediate layer 40 is located outside the outer end PB of the base layer 42 in the axial direction. From the viewpoint of effectively preventing exposure of the base layer 42 during critical running and maintaining good durability, the difference (WM-WB) between the axial width WM of the intermediate layer 40 and the axial width WB of the base layer 42 is preferably 6 mm or more, and more preferably 8 mm or more. From the viewpoint of ensuring the axial width WB of the base layer 42 and obtaining low rolling resistance, the difference (WM-WB) is preferably 14 mm or less, and more preferably 12 mm or less.

[0079] A large load acts on the tire during braking. This tends to increase the contact patch width of the tire 2. In this tire 2, the outer end PC of the cap layer 38 is located outside the reference contact edge PH in the axial direction. Even during braking, the cap layer 38 can make sufficient contact with the road surface. With this tire 2, good wet performance is obtained. From this viewpoint, it is preferable that the outer end PC of the cap layer 38 is located outside the reference contact edge PH in the axial direction.

[0080] In this tire 2, the difference (WC-WT) between the axial width WC of the cap layer 38 and the width WT of the tread 4 is preferably -10 mm or more and 10 mm or less. In other words, it is preferable that the axial width WC of the cap layer 38 is substantially equal to the width WT of the tread 4. This allows the cap layer 38 to make sufficient contact with the road surface not only during straight running but also during braking under the action of a large load. In this tire 2, good wet performance is obtained. From this viewpoint, the difference (WC-WT) is preferably -5 mm or more and 5 mm or less.

[0081] As described above, the region represented by the width WT of the tread 4 is a normal ground contact region, and the belt 14 and the band 16 are disposed in this normal ground contact region for effective reinforcement of the tread portion. The base layer 42 contributes to reducing rolling resistance, while having a lower rigidity than the cap layer 38 and the intermediate layer 40. In this tire 2, the base layer 42 is laminated on the band 16, and the band 16 is laminated on the belt 14. The base layer 42 is effectively reinforced by the belt 14 and the band 16. This base layer 42 can effectively contribute to reducing rolling resistance. From this viewpoint, it is preferable that the position of the outer end PB of the base layer 42 coincides with the position of the outer end of the band 16 in the axial direction, or that the outer end PB of the base layer 42 is located outside the outer end of the band 16. In other words, the length from the outer end of the band 16 to the outer end PB of the base layer 42 is preferably 0 mm or more. From the viewpoint of effective reinforcement of the base layer 42 and prevention of exposure, this length is preferably 4 mm or less, and more preferably 2 mm or less. In addition, when the belt 14 is wider than the band 16, the length from the outer end of the belt 14 to the outer end PB of the base layer 42 is preferably 0 mm or more from the viewpoint of reducing rolling resistance. From the viewpoint of effectively reinforcing the base layer 42 and preventing exposure, this length is preferably 4 mm or less, and more preferably 2 mm or less.

[0082] As described above, according to the present invention, a tire can be obtained that can achieve reduced rolling resistance while maintaining good wet performance and good durability. EXAMPLES

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0084] [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.

[0085] A tread was used having the configuration shown in Figure 3, with a cap layer, an intermediate layer, and a base layer. The difference between the axial width WC of the cap layer and the axial width WB of the base layer (WC-WB) was 0 mm. The difference between the axial width WM of the intermediate layer and the axial width WC of the cap layer (WM-WC) was 10 mm. The difference between the axial width WM of the intermediate layer and the axial width WB of the base layer (WM-WB) was 10 mm. The difference between the axial width WM of the intermediate layer and the axial width WB of the base layer (WM-WT) was 10 mm.

[0086] In this Example 1, the loss tangent LTc of the cap layer at 30° C. was 0.27. The loss tangent LTm of the intermediate layer at 30° C. was 0.12. The loss tangent LTb of the base layer at 30° C. was 0.10.

[0087] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the tread structure was as shown in FIG. 4 and the difference (WM-WC) and the difference (WM-WB) were as shown in Table 1 below.

[0088] [Comparative Example 2] A tire of Comparative Example 2 was obtained in the same manner as in Example 1, except that the tread structure was as shown in FIG. 5 and the difference (WC-WB) and the difference (WM-WC) were as shown in Table 1 below.

[0089] [Comparative Example 3] A tire of Comparative Example 3 was obtained in the same manner as in Example 1, except that the tread structure was as shown in FIG. 6 and the difference (WC-WB) and the difference (WM-WC) were as shown in Table 1 below.

[0090] [Comparative Example 4] A tire of Comparative Example 4 was obtained in the same manner as in Example 1, except that the tread structure was as shown in FIG. 7 and the difference (WC-WB) and the difference (WM-WB) were as shown in Table 1 below.

[0091] [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 smaller the value, the lower the rolling resistance of the tire. Rim: 16×6.5J Internal pressure: 210kPa Vertical load: 4.82kN

[0092] [Wet performance (WET)] The prototype tire was mounted on a rim (size = 16 x 6.5J) and filled with air to adjust the tire's internal pressure to 230kPa. 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 = 1.4mm). The test vehicle was traveling at a speed of 100km / h when the brakes were applied, and the distance traveled from when the brakes were applied until the vehicle came to a stop (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.

[0093] [Limit performance] The prototype tire was mounted on a rim (size = 16 x 6.5J) and filled with air to adjust the internal tire pressure to 230 kPa. The tire was then fitted to a test vehicle (passenger car). The test vehicle was driven around a circular test course with a dry road surface in an understeer state. The running speed was set at 100 km / h. After 20 laps, the wear condition of the tire buttress was checked. The results are shown in Table 1 below. "NG" indicates cases where exposure of the base layer or peeling of the tread was confirmed. "G" indicates cases where exposure of the base layer and peeling of the tread were not confirmed.

[0094] [Table 1]

[0095] As shown in Table 1, it has been confirmed that the examples can achieve a reduction in rolling resistance while maintaining good wet performance and good durability. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0096] The above-described technology capable of achieving reduced rolling resistance while maintaining good wet performance and good durability can be applied to various tires. [Explanation of symbols]

[0097] 2. Tires 4. Tread 6. Sidewall 12. Carcass 14. Belt 16...Band 34, 34a, 34b... Carcass ply 36, 36a, 36b...layer 38 Cap layer 40. Middle class 42 Base layer

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, In a radial direction, the intermediate layer is located outside the base layer, and the cap layer is located outside the intermediate layer; an outer end of the intermediate layer is located outside an outer end of the base layer, and an outer end of the cap layer is located inside an outer end of the intermediate layer in an axial direction; A difference between an axial width of the cap layer and an axial width of the base layer is −10 mm or more and 10 mm or less, The difference between the axial width of the intermediate layer and the axial width of the cap layer is 10 mm or more and 30 mm or less. tire.

2. The difference between the axial width of the base layer and the width of the tread is -10 mm or more and 10 mm or less.

2. The tire of claim 1.

3. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, 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, and a position on the outer surface of the tire that corresponds to the axial outer end of the reference contact surface is a reference contact end, In the axial direction, an outer end of the cap layer is located outside the reference ground end.

3. A tire according to claim 1 or 2.

4. A ratio of a loss tangent at 30° C. of the cap layer to a loss tangent at 30° C. of the intermediate layer is 110% or more and 250% or less. A tire according to any one of claims 1 to 3.

5. A belt is positioned radially inside the tread, and a band is positioned between the tread and the belt, The belt includes a number of belt cords arranged in parallel, The band includes a spirally wound band cord, The band is wider than the belt; In the axial direction, a position of an outer end of the base layer coincides with a position of an outer end of the band, or the outer end of the base layer is located outside the outer end of the band. A tire according to any one of claims 1 to 4.

6. The ratio of the axial width of the cap layer to the cross-sectional width of the tire is 70% or more and 90% or less. A tire according to any one of claims 1 to 5.

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