tire

Abstract

The present invention provides a tire (2) that prevents a significant reduction in wet performance due to wear and can achieve a reduction in rolling resistance. The tread (4) of the tire (2) is composed of a first tread (50) located on the first end TE1 side and a second tread (52) located on the second end TE2 side. The first tread (50) includes a first outer layer (54), an intervening layer (56), and a first inner layer (58). The second tread (52) includes a second outer layer (60) and a second inner layer (62). The first outer layer (54) is formed by a covering layer (44). The intervening layer (56) and the second outer layer (60) are formed by an intermediate layer (46) having a lower loss tangent than the covering layer (44). The first inner layer (58) and the second inner layer (62) are formed by a base layer (48) having a lower loss tangent than the intermediate layer (46). In the first tread (50), a ratio of the thickness of the first outer layer (54) to the total thickness of the first outer layer (54) and the intervening layer (56) is 0.50 or more and 0.70 or less.

Description

Technical Field

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

[0002] Using low-heat-generating rubber for the tread results in a tire with low rolling resistance. However, the grip of low-heat-generating rubber is inferior to that of heat-generating rubber, which exhibits high grip. Therefore, using low-heat-generating rubber for the tread reduces, for example, braking performance on wet roads (hereinafter also referred to as wet performance). This makes it difficult to achieve a balanced balance between rolling resistance and wet performance. Various studies are underway with the goal of reducing rolling resistance and improving wet performance (e.g., Patent Document 1 below).

[0003] For example, the tire tread disclosed in Patent Document 1 below consists of three radially laminated layers. Of these three layers, the first, outermost layer (hereinafter referred to as the cover layer) is made of a rubber that generates the most heat, considering wet performance. The third, innermost layer (hereinafter referred to as the base layer) is made of a rubber that generates the least heat, considering rolling resistance. The second, intermediate layer (hereinafter referred to as the middle layer), located between the first and third layers, is made of a rubber that generates less heat than the first layer but more heat than the third layer.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-210044 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Environmental considerations are driving the need to further reduce tire rolling resistance. Combining the intermediate layer with a rubber that heats up less easily than conventional rubber can potentially reduce rolling resistance. However, rubber that heats up less easily has poorer grip. Combining the intermediate layer with a rubber that heats up less easily increases the difference in grip between the cover layer and the intermediate layer. This can lead to wear on the tread, significantly reducing wet performance as the contact surface with the road shifts from the cover layer to the intermediate layer.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tire capable of achieving a reduction in rolling resistance while preventing a significant reduction in wet performance due to wear.

[0010] Means for solving problems

[0011] A tire according to one embodiment of the present invention includes a tread that contacts a road surface. The tread includes an overlay layer, an intermediate layer having a loss tangent at 30°C lower than that of the overlay layer, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer. The tread is oriented relative to the vehicle, with the end of the tread positioned outward in the width direction of the vehicle being the first end and the end positioned inward being the second end. The tread comprises a first tread positioned toward the first end and a second tread positioned toward the second end. The first tread includes a first outer layer, an intervening layer positioned radially inward of the first outer layer, and a first inner layer positioned radially inward of the intervening layer. The second tread includes a second outer layer and a second inner layer positioned radially inward of the second outer layer. The first outer layer is composed of the overlay layer. The intervening layer and the second outer layer are composed of the intermediate layer. The first inner layer and the second inner layer are composed of the base layer. In the first tread, a ratio of the thickness of the first outer layer to the total thickness of the first outer layer and the thickness of the intervening layer is 0.50 or more and 0.70 or less.

[0012] Preferably, in the tire, the tread is engraved with at least three circumferential grooves arranged in parallel in the axial direction, and the circumferential groove located on the outer side in the axial direction among the at least three circumferential grooves is a shoulder circumferential groove. The first tread is engraved with the shoulder circumferential groove.

[0013] Preferably, in this tire, a ratio of a loss tangent of the intermediate layer at 30° C. to a loss tangent of the cover layer at 30° C. is 0.50 or more and 0.70 or less.

[0014] Preferably, in this tire, when the tire is assembled to a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and the camber angle is set to -1°, a load of 70% of the regular load is applied to the tire as a longitudinal load, and the tire is brought into contact with a flat road surface, resulting in a standard ground contact patch. The ground contact length measured at a position corresponding to 80% of the ground contact width of the standard ground contact patch is the standard ground contact length, the standard ground contact length at the first end is the first standard ground contact length, and the standard ground contact length at the second end is the second standard ground contact length. The ratio of the first standard ground contact length to the second standard ground contact length is 0.60 or more and 0.90 or less.

[0015] Preferably, in this tire, when assembled to a regular rim and the internal pressure of the tire is adjusted to 230 kPa, the outer surface of the tire, in a meridian cross-section of the tire in an unloaded state, comprises a tread surface and a pair of side surfaces connected to one end of the tread surface. The profile of the tread surface includes a curved contour line formed by a circular arc passing through the equator of the tire. The radius of the curved contour line is not less than 500 mm and not more than 1000 mm.

[0016] Preferably, in this tire, the first tread includes a terminal portion penetrating the intervening layer and the first inner layer. The terminal portion has electrical conductivity.

[0017] Effects of the Invention

[0018] According to the present invention, it is possible to obtain a tire capable of achieving a reduction in rolling resistance while preventing a significant reduction in wet performance due to wear. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention.

[0020] Figure 2 It is an enlarged cross-sectional view showing the outline of the shoulder portion of the tire.

[0021] Figure 3 It is an enlarged cross-sectional view showing a portion of the tread.

[0022] Figure 4 This is a graphic diagram illustrating the camber angle of a tire.

[0023] Figure 5 This is a pictorial diagram illustrating the standard ground length of a standard ground plane.

[0024] Figure 6 A cross-sectional view showing the profile of the tread surface.

[0025] Figure 7 It is a cross-sectional view showing a portion of a tire according to another embodiment of the present invention.

[0026] Figure 8 This is a cross-sectional view showing a portion of the tire of Comparative Example 1.

[0027] Figure 9 It is a cross-sectional view showing a portion of the tire of Comparative Example 2. DETAILED DESCRIPTION

[0028] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0029] In this disclosure, the state in which a tire is assembled to a standard rim and its internal pressure is adjusted to the standard internal pressure, and the tire is unloaded, is referred to as the standard state. The state in which a tire is assembled to a standard rim and its internal pressure is adjusted to 230 kPa, and the tire is unloaded, is referred to as the standard state.

[0030] Unless otherwise specified in this disclosure, the dimensions and angles of various tire components are measured under standard conditions. Dimensions and angles of various components in a meridian cross-section of the tire that cannot be measured with the tire assembled on a standard rim are measured by aligning the distance between the left and right beads in a cross-section of the tire, obtained by cutting the tire along a plane including the axis of rotation, with the distance between the beads of the tire assembled on a standard rim.

[0031] Standard rims are defined by the tire's specifications. Examples include the "standard rim" under the JATMA standard, the "design rim" under the TRA standard, and the "measuring rim" under the ETRTO standard.

[0032] Standard internal pressure refers to the internal pressure specified in the tire's standards. The standard internal pressures include the "Maximum Air Pressure" in the JATMA standard, the "Maximum Pressure" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard.

[0033] Standard load refers to the load specified in the tire's standards. The standard loads include the "Maximum Load Capacity" in the JATMA standard, the "Maximum Load Capacity" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard.

[0034] In this disclosure, cross-linked rubber is a molded product of a rubber composition obtained by pressurizing and heating a rubber composition. A rubber composition is an uncross-linked rubber obtained by mixing a base rubber and a chemical in a mixer such as a Banbury mixer. Cross-linked rubber is also referred to as vulcanized rubber, and a rubber composition is also referred to as unvulcanized rubber.

[0035] Examples of 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 chemicals include carbon black, reinforcing agents such as silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of base rubber and chemicals, as well as the content of the selected chemicals, can be appropriately determined based on the specifications of various elements such as the tread and sidewall to which the rubber composition is applied.

[0036] In this disclosure, conductive rubber refers to a material with a volume resistivity of less than 1.0×10 8 Ω·cm cross-linked rubber. Non-conductive rubber refers to a rubber with a volume resistivity of 1.0×10 8 Cross-linked rubber with a conductivity of Ω·cm or greater. The conductivity of rubber is typically controlled by the carbon black content. The reinforcing agent in conductive rubber is primarily carbon black, while the reinforcing agent in non-conductive rubber is primarily silica.

[0037] In the present disclosure, when the rubber composition contains silica and carbon black as reinforcing agents, silica is considered to be the main component of the reinforcing agent as long as the mixing ratio of silica relative to the total amount of the reinforcing agent is 50% by mass or more, wherein the total amount of the reinforcing agent is expressed as the sum of the mixing amounts of silica and carbon black, and the mixing ratio of silica is expressed as the ratio of the mixing amounts of silica.

[0038] In this disclosure, the compounding amount of a chemical is expressed in parts by mass of the chemical relative to 100 parts by mass of the base rubber.

[0039] In the present disclosure, the volume resistivity of a crosslinked rubber component among the components constituting a tire is measured at 25°C according to the two-ring electrode method specified in JIS K6271. This measurement can be performed using a sheet (thickness = 2 mm) obtained by pressurizing and heating the rubber composition forming the component to be measured at 170°C for 12 minutes.

[0040] In the present disclosure, the loss tangent (also referred to as tan δ) of a crosslinked rubber component among tire components at a temperature of 30°C is measured in accordance with JIS K6394 using a viscoelastic spectrometer ("EPLEXOR Series" manufactured by GABO Corporation) under the following conditions.

[0041] Initial strain = 10%

[0042] Dynamic strain = 1%

[0043] Frequency = 10 Hz

[0044] Deformation Mode = Stretch

[0045] In this measurement, a test piece (length = 20 mm, width = 4 mm, thickness = 1 mm) was sampled from the tire. The length of the test piece aligned with the tire's circumferential direction, and the thickness aligned with the tire's radial direction. If a test piece cannot be sampled from the tire, a test piece can be sampled from a sheet of cross-linked rubber (hereinafter also referred to as a rubber sheet) obtained by pressurizing and heating the rubber composition forming the element being measured at 170°C for 12 minutes.

[0046] In this disclosure, the LAT wear index is an index for evaluating the wear resistance of a tire component composed of crosslinked rubber. The larger the LAT wear index, the better the wear resistance of the component being evaluated.

[0047] The LAT wear index corresponds to the wear resistance index defined in JIS K6264 and is expressed as the ratio of the wear volume of a reference sample to the wear volume of an evaluation sample. Wear volume is measured, for example, using a wear tester (e.g., the LAT100 wear tester manufactured by VMI) under conditions of a load of 40 N and a slip angle of 6°. The reference sample can be appropriately selected depending on the factors being evaluated.

[0048] Figure 1 A portion of a tire 2 according to one embodiment of the present invention is shown. The tire 2 is a tire for passenger cars. Figure 1 1 shows a portion of a cross section of the tire 2 (hereinafter also referred to as a meridian cross section) taken along a plane including the rotation axis of the tire 2 . Figure 1 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 1 The direction of the paper surface is the circumferential direction of the tire 2.

[0049] Figure 1 In FIG, the one-dot chain line EL is the equatorial plane EL of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane EL, except for decorations such as tread patterns, designs, and characters engraved on its outer surface, and the internal structure of the tread described later.

[0050] Figure 1 In the figure, a tire 2 is assembled to a rim R. Rim R is a standard rim. The interior of tire 2 is filled with air to adjust the internal pressure of tire 2. The tire 2 assembled to rim R is also called a tire-rim assembly. The tire-rim assembly includes rim R and tire 2 assembled to rim R.

[0051] Figure 1 In FIG, the position indicated by symbol PW is the axial outer end of the tire 2. When a decoration such as a pattern or letter is on the outer surface, the outer end PW is specified based on a virtual outer surface assuming no decoration.

[0052] Figure 1 In the diagram, the length denoted by WA is the maximum width of the tire 2, or the cross-sectional width (see JATMA, etc.). The cross-sectional width WA of the tire 2 is the axial distance from one outer end PW to the other outer end PW. The outer end PW is the location where the tire 2 has its maximum width (hereinafter referred to as the maximum width location). The cross-sectional width WA is measured on a tire 2 in a standard state.

[0053] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinchers 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a reinforcing layer 16 , a pair of scuff layers 18 , and an inner liner 20 .

[0054] The outer surface of the tread 4 is in contact with the road surface. The tread 4 is engraved with grooves 22. This constitutes a tread pattern.

[0055] The grooves 22 constituting the tread pattern include circumferential grooves 24 extending continuously in the circumferential direction. In the tire 2, at least three circumferential grooves 24 arranged in parallel in the axial direction are engraved on the tread 4. Thus, the tread 4 constitutes at least four land portions 26. Figure 1 In the tire 2 shown, four circumferential grooves 24 are engraved in the tread 4 to form five land portions 26 .

[0056] The tread 4 of the tire 2 includes a tread body 28 and a pair of wing portions 30. Each wing portion 30 is located axially outside the tread body 28. The wing portions 30 connect the tread body 28 and the sidewall 6. The wing portions 30 are formed of a cross-linked rubber that takes bonding properties into consideration.

[0057] Figure 1 In the figure, the position indicated by the symbol TE is one end of the tread 4. The tire 2 is assigned the direction of the tread 4 relative to the vehicle. Figure 1 In the paper, the end TE of the tread 4 on the left side is referred to as the first end TE1, and the end TE of the tread 4 on the right side is referred to as the second end TE2. When the tire 2 is mounted on a vehicle, of the two ends TE of the tread 4, the first end TE1 of the tread 4 is positioned outward in the width direction of the vehicle. The second end TE2 of the tread 4 is positioned inward in the width direction of the vehicle.

[0058] Figure 1 , the position indicated by symbol PE is the equator of the tire 2. The equator PE is the intersection of the outer surface of the tread 4 and the equatorial plane EL. When the groove 22 is present on the equatorial plane EL, the equator PE is specifically specified based on the virtual outer surface of the tread 4, assuming that the groove 22 is absent.

[0059] Figure 1 , the position indicated by 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.

[0060] The contact patch used to identify position PH is obtained, for example, using a contact patch shape measuring device (not shown). This contact patch is obtained by applying a longitudinal load of 70% of the standard load to the tire 2 in a standard state with the camber angle set to 0°, and then placing the tire 2 in contact with a flat road surface. Although not shown, the contact patch obtained in this manner in the tire 2 is referred to as the reference contact patch, and the position on the outer surface of the tread 4 corresponding to the axially outer end of this reference contact patch is referred to as position PH. In the tire 2, this position PH is referred to as the reference contact end. Figure 1 In FIG. 1 , the length represented by the symbol WH is the ground width of the reference ground plane. The ground width WH is the axial distance from one reference ground end PH to another reference ground end PH. The ground width WH is measured at the reference ground plane.

[0061] Each sidewall 6 is connected to one end TE of the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the one end TE of the tread 4 toward the clinch 8 along the carcass 12. The sidewall 6 is formed of a cross-linked rubber having a high cut resistance.

[0062] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 is in contact with the rim R. The clinch 8 is formed of a cross-linked rubber in consideration of wear resistance.

[0063] Each bead 10 is located axially inside the clinch portion 8. The bead 10 includes a core 32 and an apex 34. Although not shown, the core 32 includes a steel wire.

[0064] The apex 34 is located radially outside the core 32. The apex 34 tapers outward. The apex 34 is formed of a cross-linked rubber having high rigidity.

[0065] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinch portions 8. The carcass 12 is spanned between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0066] The carcass 12 includes at least one carcass ply 36. The carcass 12 of the tire 2 is composed of two carcass plies 36. The carcass ply 36 located radially inward of the tread 4 is a first carcass ply 38, and the carcass ply 36 located outward of the first carcass ply 38 is a second carcass ply 40. From the perspective of weight reduction, the carcass 12 may be composed of a single carcass ply 36.

[0067] The first carcass ply 38 includes a first ply main body 38 a spanning between one core 32 and the other core 32 , and a pair of first folded portions 38 b connected to the first ply main body 38 a and folded around each core 32 from the axial inside toward the outside.

[0068] The second carcass ply 40 includes a second ply main body 40 a spanning between one core 32 and the other core 32 , and a pair of second folded portions 40 b connected to the second ply main body 40 a and folded from the axial inside toward the outside around each core 32 .

[0069] Although not shown, the carcass ply 36 includes a plurality of carcass cords arranged in parallel. Each carcass cord intersects the equatorial plane EL. The carcass cords are made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0070] The belt layer 14 is located radially inward of the tread 4. The belt layer 14 is laminated to the carcass 12 from the outer side in the radial direction. Figure 1 In the figure, the length indicated by symbol WR is the axial width of the belt layer 14. The axial width WR is the axial distance from one end to the other end of the belt layer 14. In the tire 2, the axial width WR of the belt layer 14 is not less than 65% and not more than 85% of the cross-sectional width WA.

[0071] The belt layer 14 is composed of at least two layers 42 laminated in the radial direction. The belt layer 14 of the tire 2 is composed of two layers 42 laminated in the radial direction. Of the two layers 42, the layer 42 located on the inner side is the inner layer 42a, and the layer 42 located on the outer side is the outer layer 42b. Figure 1 As shown, the width of the inner layer 42a is wider than that of the outer layer 42b. The length from one end of the outer layer 42b to one end of the inner layer 42a is 3 mm to 10 mm.

[0072] Although not shown, the inner layer 42a and the outer layer 42b each include a plurality of parallel belt cords. Each belt cord is inclined with respect to the equatorial plane EL. The belt cords are made of steel.

[0073] The reinforcing layer 16 is located between the tread 4 and the belt 14 in the radial direction. The reinforcing layer 16 is laminated to the belt 14 on the inner side of the tread 4.

[0074] Although not shown, the reinforcement layer 16 includes a helically wound reinforcement cord. The reinforcement cord extends substantially in the circumferential direction. Specifically, the angle formed by the reinforcement cord with respect to the circumferential direction is 5° or less. The reinforcement layer 16 has a seamless structure. In this tire 2, a cord formed from organic fibers is used as the reinforcement cord. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0075] The tire 2's reinforcement layer 16 is formed from a single, opposing reinforcement layer with both ends spanning the equator PE. The reinforcement layer 16 is wider than the belt 14. The length from one end of the belt 14 to one end of the reinforcement layer 16 is between 3 mm and 7 mm. The reinforcement layer 16 covers the entire belt 14. The reinforcement layer 16 may also include a pair of axially separated edge reinforcement layers that cover one end of the entire reinforcement layer and one end of the belt 14. The reinforcement layer 16 may consist solely of a pair of edge reinforcement layers.

[0076] Each anti-scuff layer 18 is located radially inward of the bead 10. The anti-scuff layer 18 is in contact with the rim R. The anti-scuff layer 18 of the tire 2 is composed of cloth and rubber impregnated in the cloth.

[0077] The inner liner 20 is located inside the carcass 12. The inner liner 20 forms the inner surface of the tire 2. The inner liner 20 is made of a cross-linked rubber having a low gas permeability coefficient. The inner liner 20 maintains the internal pressure of the tire 2.

[0078] Figure 2 express Figure 1 A portion of a tire 2 is shown. Figure 2 In the figure, the left and right directions are the axial directions of the tire 2, and the up and down directions are the radial directions of the tire 2. Figure 2 The direction of the paper surface is the circumferential direction of the tire 2.

[0079] Figure 2 The outline of the shoulder portion of the tire 2 in a meridian cross section is shown. Figure 2 The profile shown is obtained by measuring the outer surface shape of the tire 2 in a standard state using a displacement sensor. Figure 2 The figure shows the outline of the outer surface of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0080] In a meridian cross-section, the profile of the outer surface of the tire 2 (hereinafter referred to as the tire outer surface TS) is formed by connecting multiple contour lines formed by straight lines or circular arcs. In this disclosure, contour lines formed by straight lines or circular arcs are simply referred to as contour lines. Contour lines formed by straight lines are referred to as linear contour lines, and contour lines formed by circular arcs are referred to as curved contour lines.

[0081] The tire outer surface TS includes a tread surface T and a pair of side surfaces S connected to one end of the tread surface T. In a meridian cross-section, the contour of the tread surface T includes multiple curved contour lines with different radii. In this tire 2, the curved contour line with the smallest radius among the multiple curved contour lines included in the contour of the tread surface T is located at the end 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 is formed by the arc with the smallest radius among the multiple curved contour lines included in the contour of the tread surface T. The end of the tread surface T includes a curved portion, which is a curved contour line connected to the side surface S. Figure 2 The curved portion is represented by the symbol RS.

[0082] In the profile of the tire's outer surface TS, the curved portion RS and the contour line adjacent to the axially inner side thereof (hereinafter referred to as the inner adjacent contour line NT) meet at a tangent point CT. The curved portion RS and the contour line adjacent to the axially outer side thereof, which constitutes the profile of the side surface S (hereinafter referred to as the outer adjacent contour line NS), meet at a tangent point CS. The profile of the tire's outer surface TS includes the inner adjacent contour line NT, which is located axially inward of the curved portion RS and in contact with the curved portion RS, and the outer adjacent contour line NS, which is located axially outward of the curved portion RS and in contact with the curved portion RS.

[0083] Figure 2 In the figure, solid line LT is a tangent to the curved portion RS at the point of tangency CT between the inner adjacent contour line NT and the curved portion RS. Solid line LS is a tangent to the curved portion RS at the point of tangency CS between the outer adjacent contour line NS and the curved portion RS. The position indicated by symbol PT is the intersection of tangent lines LT and LS. In this tire 2, this intersection point PT is the tread reference end.

[0084] Figure 1 In the figure, the length indicated by the two arrows WT is the tread width. This tread width WT is the axial distance from one tread reference end PT to the other tread reference end PT. In this tire 2, the ratio of the tread width WT to the cross-sectional width WA (WT / WA) is 70% or more and 90% or less. The ratio of the contact patch width WH of the reference contact patch to the tread width WT is 70% or more and 90% or less.

[0085] As previously mentioned, the tread 4 of the tire 2 is engraved with four circumferential grooves 24. In the tire 2, the arrangement, groove depth, and groove width of the four circumferential grooves 24 are not particularly limited. Conventional arrangements, groove depths, and groove widths of the circumferential grooves of a tire can be applied to the tread 4.

[0086] In this tire 2, the circumferential grooves 24 located axially outward of the four circumferential grooves 24 are shoulder circumferential grooves 24s. The circumferential grooves 24 located inward of the shoulder circumferential grooves 24s are intermediate circumferential grooves 24m. In this tire 2, the four circumferential grooves 24 consist of a pair of shoulder circumferential grooves 24s and a pair of intermediate circumferential grooves 24m. The pair of shoulder circumferential grooves 24s and the pair of intermediate circumferential grooves 24m are symmetrically arranged with respect to the equatorial plane EL. The circumferential grooves 24 may also be arranged asymmetrically with respect to the equatorial plane EL.

[0087] As described above, the tread 4 of the tire 2 is composed of five land portions 26. Among the five land portions 26, the axially outer land portion 26 is the shoulder land portion 26s. The land portion 26 axially inward of the shoulder land portion 26s is the middle land portion 26m. The land portion 26 located between the left and right middle land portions 26m is the center land portion 26c. This center land portion 26c is located on the equatorial plane EL.

[0088] Figure 1 In the diagram, the length indicated by the double arrows WC is the axial width of the center land portion 26c. Axial width WC is the axial distance from the boundary between the outer surface of the middle circumferential groove 24m and the center land portion 26c on the first end TE1 side to the boundary between the outer surface of the middle circumferential groove 24m and the center land portion 26c on the second end TE2 side. The length indicated by the double arrows WM is the axial width of the center land portion 26m. Axial width WM is the axial distance from the boundary between the outer surface of the middle circumferential groove 24m and the center land portion 26m to the boundary between the outer surface of the shoulder circumferential groove 24s and the center land portion 26m. The length indicated by the double arrows WS is the axial width of the shoulder land portion 26s. Axial width WS is the axial distance from the boundary between the outer surface of the shoulder circumferential groove 24s and the shoulder land portion 26s to the tread reference end PT.

[0089] In this tire 2, from the perspective of achieving a balanced balance between steering stability and drainage, the ratio of the axial width WC of the center land portion 26c to the tread width WT (WC / WT) is preferably 0.08 or more and 0.20 or less. The ratio of the axial width WS of the shoulder land portion 26s to the tread width WT (WS / WT) is preferably 0.20 or more and 0.30 or less. Furthermore, the ratio of the axial width WM of the middle land portion 26m to the tread width WT (WM / WT) is set in consideration of the ratios (WC / WT) and (WS / WT).

[0090] The tread 4 of this tire 2 (specifically, the tread body 28) includes a cover layer 44, an intermediate layer 46, and a base layer 48. The cover layer 44, intermediate layer 46, and base layer 48 are each formed from a cross-linked rubber having different heat generation properties. In this tire 2, the loss tangent LTm of the intermediate layer 46 at 30°C is lower than the loss tangent LTc of the cover layer 44 at 30°C. The loss tangent LTb of the base layer 48 at 30°C is lower than the loss tangent LTm of the intermediate layer 46 at 30°C. In this tire 2, the cover layer 44 is most susceptible to heat generation, contributing to the tire 2's grip. The base layer 48 is least susceptible to heat generation, contributing to reduced rolling resistance of the tire 2.

[0091] The intermediate layer 46 of the tire 2 has a heat generation characteristic intermediate between that of the cover layer 44 and that of the base layer 48. By configuring the intermediate layer 46 to have a loss tangent LTm close to the loss tangent LTc of the cover layer 44, a tread 4 that emphasizes grip can be obtained. By configuring the intermediate layer 46 to have a loss tangent LTm close to the loss tangent LTb of the base layer 48, a tread 4 that emphasizes reduced rolling resistance can be obtained.

[0092] like Figure 1 As shown, the tread body 28 of the tire 2 is composed of a three-layer laminate on the first end TE1 side and a two-layer laminate on the second end TE2 side. In this tire 2, the portion of the laminate comprising the three layers on the first end TE1 side is a first tread 50, and the portion of the laminate comprising the two layers on the second end TE2 side is a second tread 52. The tread 4 is composed of the first tread 50 located on the first end TE1 side and the second tread 52 located on the second end TE2 side.

[0093] Figure 1 , the position indicated by symbol PB is the boundary between the first tread 50 and the second tread 52 of the tread surface T. Figure 1 In FIG. 1 , the length indicated by the two arrows WT1 is the axial distance from the reference ground terminal PH on the first end TE1 side to the boundary PB.

[0094] The first tread 50 includes a first outer layer 54, an intervening layer 56, and a first inner layer 58. The outer surface of the first outer layer 54 forms a part of the tread surface T. The intervening layer 56 is located radially inside the first outer layer 54. The first inner layer 58 is located radially inside the intervening layer 56. Figure 1 As shown, the first outer layer 54 is laminated to the intervening layer 56. The intervening layer 56 is laminated to the first inner layer 58. The first inner layer 58 is laminated to the reinforcement layer 16.

[0095] The second tread 52 includes a second outer layer 60 and a second inner layer 62. The outer surface of the second outer layer 60 becomes a part of the tread surface T. The second inner layer 62 is located radially inward of the second outer layer 60. Figure 1 As shown, the second outer layer 60 is laminated to the second inner layer 62. The second inner layer 62 is laminated to the reinforcement layer 16.

[0096] In the tire 2, the first outer layer 54 of the first tread 50 is formed by the cover layer 44. The intervening layer 56 of the first tread 50 and the second outer layer 60 of the second tread 52 are formed by the intermediate layer 46. The first inner layer 58 of the first tread 50 and the second inner layer 62 of the second tread 52 are formed by the base layer 48.

[0097] In this tire 2, the second tread 52 includes a terminal portion 64 formed of conductive rubber. The terminal portion 64 extends through the second outer layer 60 and the second inner layer 62 of the second tread 52. The outer end of the terminal portion 64 forms part of the tread surface T. The inner end of the terminal portion 64 is connected to the reinforcing layer 16. The terminal portion 64 helps ensure the electrical conductivity of the tire 2.

[0098] As described above, the tread 4 contacts the road surface and contributes to the grip. The contribution of the tread 4 to the grip is higher on the first end TE1 side than on the second end TE2 side.

[0099] The tread surface T of this tire 2 includes a portion formed by the intermediate layer 46 that is detrimental to exerting grip. However, in this tire 2, the first outer layer 54 of the first tread 50 on the first end TE1 side is formed by the covering layer 44 that is designed to exert grip. In this tire 2, regardless of whether the tread surface T includes a portion formed by the intermediate layer 46 that is detrimental to exerting grip, the tread 4 contributes to exerting grip. This tire 2 can ensure good wet performance. Since the tread 4 can be constructed to include a large amount of intermediate layers 46 that can contribute to reducing rolling resistance, this tire 2 can reduce rolling resistance.

[0100] like Figure 1 As shown, in this tire 2 , among the four circumferential grooves 24 engraved in the tread 4 , the shoulder circumferential grooves 24 s located on the outer side in the axial direction are engraved in the first tread 50 . Figure 3 express Figure 1 A portion of the cross section of the tire 2 is shown. Figure 3 3 shows a portion of the shoulder circumferential groove 24s engraved on the first tread 50. Provided at the bottom of the shoulder circumferential groove 24s is a slip sign 66 (also referred to as a wear indicator).

[0101] Figure 3In the figure, the double arrows TG represent the thickness of the first outer layer 54. The double arrows TK represent the thickness of the intervening layer 56. The double arrows TC represent the total thickness of the thickness TG of the first outer layer 54 and the thickness TK of the intervening layer 56. The thickness TG of the first outer layer 54, the thickness TK of the intervening layer 56, and the total thickness TC are measured within the range from the boundary between the outer surface of the land portion 26 and the circumferential groove 24 (in other words, the edge of the circumferential groove 24) to a position 5 mm away, where the thickness variation of each layer is suppressed. Furthermore, if the first tread 50 is engraved with multiple circumferential grooves 24, the thickness of the first outer layer 54, the thickness of the intervening layer 56, and the total thickness are measured at each circumferential groove 24, and the thickness TG of the first outer layer 54, the thickness TK of the intervening layer 56, and the total thickness TC are expressed based on the average value.

[0102] In the tire 2 , the ratio (TG / TC) of the thickness TG of the first outer layer 54 in the first tread 50 to the total thickness TC of the thickness TG of the first outer layer 54 and the thickness TK of the intervening layer 56 is 0.50 or more and 0.70 or less.

[0103] Since the ratio (TG / TC) is at least 0.50, the thickness of the first outer layer 54, which contributes to the development of grip, can be sufficiently ensured. This tire 2 can suppress a significant decrease in wet performance due to wear. From this perspective, the ratio (TG / TC) is preferably at least 0.53, and more preferably at least 0.55.

[0104] Since the ratio (TG / TC) is 0.70 or less, the thickness of the intervening layer 56 formed by the intermediate layer 46, which contributes to reducing rolling resistance, can be effectively ensured. This tire 2 can suppress the effect of the first outer layer 54 formed by the cover layer 44, which is prone to heat generation, on rolling resistance. From this perspective, the ratio (TG / TC) is preferably 0.67 or less, and more preferably 0.65 or less.

[0105] In this tire 2, the first tread 50 on the first end TE1 side includes a first outer layer 54 formed of an overlay layer 44. The ratio (TG / TC) of the thickness TG of the first outer layer 54 to the total thickness TC of the thickness TG of the first outer layer 54 and the thickness TK of the intervening layer 56 is 0.50 or more and 0.70 or less. This tire 2 prevents a significant decrease in wet performance due to wear and can achieve reduced rolling resistance.

[0106] Figure 3 In FIG, the double arrows DG indicate the groove depth of the circumferential groove 24. The groove depth DG is represented by the distance from the tread surface T to the slip mark 66. The groove depth DG is also referred to as the effective groove depth.

[0107] In the tire 2, from the perspective of balancing wet performance and rolling resistance, the ratio of the total thickness TC of the thickness TG of the first outer layer 54 and the thickness TK of the intervening layer 56 to the groove depth DG of the circumferential groove 24 (TC / DG) is preferably greater than 0.80 and less than 1.00.

[0108] like Figure 1 As shown, in the tire 2, one end of the first outer layer 54 on the first end TE1 side (hereinafter referred to as the first end 68a of the first outer layer 54) is axially located outside the reference ground contact end PH. The position of the first end 68a of the first outer layer 54 is axially almost identical to the position of the tread reference end PT. The first end 68a of the first outer layer 54 may also be axially located inside the tread reference end PT. In this case, from the perspective of effectively exerting wet performance, the axial distance from the tread reference end PT to the first end 68a of the first outer layer 54 is preferably 5 mm or less. The first end 68a of the first outer layer 54 may also be axially located outside the tread reference end PT. In this case, the position of the first end 68a of the first outer layer 54 may be determined in consideration of the influence on wet performance and rolling resistance.

[0109] like Figure 1 As shown, in this tire 2, among the four circumferential grooves 24 engraved in the tread 4, the shoulder circumferential groove 24s located axially outward is engraved in the first tread 50. One end of the first outer layer 54 located at the boundary PB between the first tread 50 and the second tread 52, that is, on the second end TE2 side (hereinafter referred to as the second end 68b of the first outer layer 54) is located inward of the shoulder circumferential groove 24s located axially on the first end TE1 side.

[0110] As previously mentioned, in this tire 2, the position of the first end 68a of the first outer layer 54 is substantially aligned axially with the position of the tread reference end PT. The portion of the tread 4 between the tread reference end PT and the shoulder circumferential groove 24s constitutes the shoulder land portion 26s. In this tire 2, the outer surface of the shoulder land portion 26s on the first end TE1 side, which contributes most to grip, is substantially formed by the first outer layer 54. This tire 2 ensures excellent wet performance.

[0111] The tire 2 can control wet performance and rolling resistance by adjusting the position of the boundary PB between the first tread 50 and the second tread 52. The rolling resistance of the tire 2 is reduced by bringing the boundary PB closer to the first end TE1 of the tread 4. From this point of view, the ratio (WT1 / WH) of the axial distance WT1 from the reference ground contact end PH on the side of the first end TE1 to the boundary PB relative to the ground contact width WH of the reference ground contact surface is preferably 95% or less, more preferably 85% or less. In contrast, the wet performance of the tire 2 is improved by bringing the boundary PB closer to the second end TE2 of the tread 4. From this point of view, the ratio (WT1 / WH) is preferably 30% or more, more preferably 40% or more. From the viewpoint of uniformly adjusting the wet performance and rolling resistance, the ratio (WT1 / WH) is particularly preferably 55% or more and 75% or less.

[0112] As described above, the loss tangent LTm of the intermediate layer 46 at 30°C is lower than the loss tangent LTc of the cover layer 44 at 30°C. Specifically, the ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 46 at 30°C to the loss tangent LTc of the cover layer 44 at 30°C is preferably 0.50 or more and 0.70 or less.

[0113] By setting the ratio (LTm / LTc) to 0.50 or greater, variations in the gripping force of the cover layer 44 and the gripping force of the intermediate layer 46 can be effectively suppressed. This tire 2 can suppress a significant decrease in wet performance due to wear. From this perspective, the ratio (LTm / LTc) is more preferably 0.53 or greater, and even more preferably 0.55 or greater.

[0114] By setting the ratio (LTm / LTc) to 0.70 or less, the intermediate layer 46 can effectively contribute to reducing rolling resistance. From this viewpoint, the ratio (LTm / LTc) is preferably 0.67 or less, and more preferably 0.65 or less.

[0115] In this tire 2, the loss tangent LTb of the base layer 48 at 30°C is preferably 0.11 or less. This is because the base layer 48 effectively contributes to reducing rolling resistance. From this perspective, the loss tangent LTb is more preferably 0.10 or less, and even more preferably 0.09 or less. In this tire 2, the lower the loss tangent LTb of the base layer 48, the better, so no lower limit is set.

[0116] The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.15 or less. This is because the intermediate layer 46 effectively contributes to reducing rolling resistance. From this perspective, the loss tangent Ltm is more preferably 0.14 or less, and even more preferably 0.13 or less. The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.11 or greater. This is because the intermediate layer 46 ensures the necessary rigidity and effectively contributes to improving wet performance. From this perspective, the loss tangent LTm is more preferably 0.12 or greater.

[0117] The loss tangent LTc of the cover layer 44 at 30°C is preferably not less than 0.15. This is because the cover layer 44 can help improve wet performance. From this point of view, the loss tangent LTc is more preferably not less than 0.16, and further preferably not less than 0.17. The cover layer 44 is in contact with the road surface. From the perspective of improving wet performance, the higher the loss tangent LTc, the better. However, a high loss tangent LTc will cause heat to form. The heated cover layer 44 may cause the temperature of the intermediate layer 46 to rise above a predetermined temperature. From the perspective of maintaining a stable temperature state of the entire tread 4 and being able to maintain low rolling resistance, the loss tangent LTc of the cover layer 44 at 30°C is preferably not more than 0.30, more preferably not more than 0.28, and further preferably not more than 0.27.

[0118] Figure 4 The figure shows a state of a tire 2 mounted on a vehicle (not shown). Figure 4 The left side of the paper is the outer side in the width direction of the vehicle, and the right side is the inner side in the width direction of the vehicle.

[0119] like Figure 4 As shown, the tire 2 is usually mounted on a vehicle so that its equatorial plane EL is inclined with respect to the road surface. Figure 4 In the diagram, the solid line BL is a straight line perpendicular to the flat road surface. Angle θ is the angle formed by the equatorial plane EL with respect to the straight line BL. This angle θ is also called the camber angle. Figure 4 The tire 2 shown is mounted on the vehicle so that its upper portion is located inward of its lower portion in the vehicle width direction relative to the equatorial plane EL. The camber angle of the tire 2 mounted in this manner is also called negative camber and is represented by a negative angle.

[0120] Figure 5 An image of the contact patch of the tire 2 is shown in FIG. Figure 5 , the up-down direction corresponds to the circumferential direction of the tire 2 , and the left-right direction corresponds to the axial direction of the tire 2 . Figure 5 The left side of the paper is the outer side in the width direction of the vehicle, in other words, the first end TE1 side of the tread 4. The right side of the paper is the inner side in the width direction of the vehicle, in other words, the second end TE2 side of the tread 4.

[0121] This contact patch is obtained, for example, using a contact patch shape measuring device (not shown). This contact patch is obtained by applying a longitudinal load of 70% of the standard load to a standard tire 2 with its camber angle θ set to -1°, and then placing the tire 2 in contact with a flat road surface. In this disclosure, this contact patch is referred to as the standard contact patch.

[0122] Figure 5 In the figure, the dashed line CL represents the axial centerline of the standard contact patch. The solid line ML is a straight line passing through the axial outer end of the standard contact patch and parallel to the centerline CL. The solid line AL is located between the line ML and the centerline CL and is parallel to both lines ML and CL. The two arrows A100 indicate the axial distance from the centerline CL to the line ML. This distance A100 corresponds to half the maximum contact patch width of the standard contact patch. The two arrows A80 indicate the axial distance from the centerline CL to the line AL. In this tire 2, the ratio of the distance A80 to the distance A100 is set to 80%. That is, the line AL represents a position corresponding to 80% of the maximum contact patch width of the standard contact patch. The two arrows L indicate the length of the intersection of the plane including the line AL and the standard contact patch. This intersection length L is the contact patch length measured at a position corresponding to 80% of the contact patch width of the standard contact patch and is also referred to as the standard contact patch length. The standard contact patch length L on the first end TE1 side is referred to as the first standard contact patch length L1, and the standard contact patch length L on the second end TE2 side is referred to as the second standard contact patch length L2.

[0123] In the tire 2 , the ratio ( L1 / L2 ) of the first standard ground contact length L1 to the second standard ground contact length L2 is preferably 0.60 or more and 0.90 or less.

[0124] By setting the ratio (L1 / L2) to 0.60 or greater, changes in the contact patch shape relative to wheel alignment can be effectively suppressed. This results in a stable contact patch shape, which can suppress the occurrence of uneven wear. This tire 2 prevents significant degradation of wet performance due to wear and achieves reduced rolling resistance. From this perspective, the ratio (L1 / L2) is more preferably 0.65 or greater, and even more preferably 0.70 or greater.

[0125] By setting the ratio (L1 / L2) to 0.90 or less, the tread 4 can fully demonstrate its functions. This tire 2 achieves a balanced balance between cornering stability and straight-line stability. This tire 2 can exhibit excellent wet performance while maintaining low rolling resistance. From this perspective, the ratio (L1 / L2) is more preferably 0.85 or less, and even more preferably 0.80 or less.

[0126] Figure 6 express Figure 1A portion of a tire 2 is shown. Figure 6 In FIG, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. Figure 6 The direction perpendicular to the paper surface is the circumferential direction of the tire 2.

[0127] Figure 6 ] The profile of the tread surface T of the tire 2 in a meridian cross section is shown in FIG. Figure 6 The outline shown is the same as Figure 2 The profile shown is similarly obtained by measuring the outer surface shape of the tire 2 in a standard state using a displacement sensor. Figure 6 : shows the profile of the tread surface T of the tire 2 in the meridian cross section of the tire 2 in the standard state.

[0128] The tread surface T of the tire 2 is divided into a plurality of axially parallel regions in a meridian cross-section. These regions include a crown region Cr, a pair of middle regions Mi, and a pair of side regions Sd. The crown region Cr is axially central. The crown region Cr includes the equator PE. Each middle region Mi is axially outward of the crown region Cr. Each side region Sd is axially outward of the middle region Mi.

[0129] Figure 6 The position denoted by symbol CM is the boundary between the crown region Cr and the middle region Mi. The position denoted by symbol MS is the boundary between the middle region Mi and the side region Sd. Symbol SE is the outer end of the side region Sd. The outer end SE can also be the aforementioned tangent point CT.

[0130] As previously described, the profile of the tread surface T includes multiple curved contour lines with different radii. The contours of each region are represented by curved contour lines. In this tire 2, the curved contour line representing the profile of the crown region Cr is also referred to as the central contour line. The curved contour line representing the profile of the middle region Mi is also referred to as the intermediate contour line. The curved contour lines representing the profile of the side regions Sd are also referred to as the side contour lines. The multiple curved contour lines included in the profile of the tread surface T include the central contour line, a pair of intermediate contour lines, and a pair of side contour lines.

[0131] Although not shown, the center of the central outline is located on the equatorial plane EL. Figure 6 In the figure, the one-way arrow represented by symbol Rc is the radius of the central contour line. The intermediate contour line and the central contour line meet at the boundary CM. Figure 6 The one-way arrow represented by symbol Rm is the radius of the middle contour line. The side contour line is connected to the middle contour line at the boundary MS. Figure 6 The one-way arrow represented by the symbol Rd is the radius Rd of the side profile line.

[0132] In this tire 2, the radius Rm of the middle contour line is smaller than the radius Rc of the central contour line, and the radius Rd of the side contour line is smaller than the radius Rm of the middle contour line. Thus, the contour lines are smoothly connected to form a tread 4 that can fully exert its functions. This tire 2 can balance cornering stability and straight-line driving stability. From this perspective, the ratio of the radius Rm of the middle contour line to the radius Rc of the central contour line (Rm / Rc) is preferably greater than 0.50 and preferably less than 0.54. The ratio of the radius Rd of the side contour line to the radius Rc of the central contour line (Rd / Rc) is preferably greater than 0.20 and preferably less than 0.24.

[0133] In this tire 2, the radius Rc of the central contour line is preferably at least 500 mm and no more than 1000 mm. This achieves a contact patch shape in which the ratio (L1 / L2) of the first standard contact patch length L1 to the second standard contact patch length L2 is set within the aforementioned range. Because the tread 4 can fully exert its function, this tire 2 prevents a significant decrease in wet performance due to wear and achieves reduced rolling resistance. From this perspective, the radius Rc of the central contour line is more preferably at least 550 mm, and even more preferably at least 600 mm. The radius Rc of the central contour line is more preferably at most 950 mm, and even more preferably at most 900 mm. In this tire 2, the radius Rc of the central contour line is the radius of an arc centered on the equatorial plane EL and passing through the left and right edges of the central land portion 26c and the equator PE. In a tread having circumferential grooves engraved on the equatorial plane EL, the radius Rc of the central contour line is the radius of an arc centered on the equatorial plane EL and passing through the edges of the land portions located on both sides of the circumferential grooves.

[0134] In the tire 2, the cover layer 44 and the intermediate layer 46 coexist in the first tread 50. If the wear resistance of the cover layer 44 and the wear resistance of the intermediate layer 46 are discrete, there is a possibility that the wear amount of the two will differ. In this case, there is a possibility that a height difference will occur near the boundary between the cover layer 44 and the intermediate layer 46, which will damage the appearance of the tire 2. From the perspective of maintaining a good appearance, it is preferred that the LAT wear index LATc of the cover layer 44 and the LAT wear index LATm of the intermediate layer 46 are of the same level. Specifically, the difference (LATc-LATm) between the LAT wear index LATc of the cover layer 44 and the LAT wear index LATm of the intermediate layer 46 is preferably greater than -10 and less than 10. The difference (LATc-LATm) is more preferably greater than -5 and less than 5. The difference (LATc-LATm) is further preferably 0.

[0135] Figure 7 A portion of a tire 72 according to another embodiment of the present invention is shown. Figure 7 A meridian cross section of the tire 72 is shown. Figure 7 In FIG, the left-right direction is the axial direction of the tire 72, and the up-down direction is the radial direction of the tire 72. Figure 7 The direction perpendicular to the paper surface is the circumferential direction of the tire 72.

[0136] The tire 72 is in addition to Figure 1 The tire 2 shown has the same configuration as the tire 2 except that the arrangement of the terminal portion 64 is different. Figure 1 The tire 2 shown has the same structure. Figure 7 In relation to Figure 1 The same components as those of the tire 2 are denoted by the same reference numerals, and their description is omitted.

[0137] The tread 4 of the tire 72 is also Figure 1 The tread 4 of the tire 2 shown is similarly composed of a first tread 50 and a second tread 52 . Figure 1 The tire 2 shown has a terminal portion 64 on the second tread 52, while the tire 72 has a terminal portion 64 on the first tread 50. Figure 7 As shown, the terminal portion 64 passes through the intervening layer 56 and the first inner layer 58. The terminal portion 64 is connected to the first outer layer 54 at the outer end. The terminal portion 64 is connected to the reinforcement layer 16 at the inner end.

[0138] As previously mentioned, the first outer layer 54 is formed of the cover layer 44. Although not described in detail, the reinforcing agent of the rubber composition used for the cover layer 44 contains carbon black as a main component from the viewpoint of exerting high grip. Therefore, the cover layer 44 has electrical conductivity. In other words, the cover layer 44 is formed of conductive rubber. Since the first outer layer 54 and the reinforcing layer 16 are connected by the terminal portion 64, the tire 72 and Figure 1 The tire 2 shown can similarly ensure electrical conductivity. The outer end of the terminal portion 64 is covered by the first outer layer 54, so the terminal portion 64 of the tire 72 is not exposed on the tread surface T. Therefore, until the first outer layer 54 wears away and disappears, the reduction in the appearance quality of the tread 4 caused by the terminal portion 64 can be suppressed. Even if the tread 4 is worn, its appearance can be well maintained. Since a stable ground contact shape can be obtained even if the tread 4 is worn, the tread 4 can fully exert its function. The tire 72 prevents the reduction in appearance quality and the significant reduction in wet performance due to wear and tear and can achieve a reduction in rolling resistance.

[0139] As described above, according to the present invention, it is possible to obtain a tire capable of achieving a reduction in rolling resistance while preventing a significant reduction in wet performance due to wear.

[0140] [Example]

[0141] The present invention will be further described in detail below with reference to examples, etc. However, the present invention is not limited to the examples.

[0142] [Example 1]

[0143] Get equipped Figure 1 The basic structure shown in FIG. 1 is provided with a pneumatic tire for a passenger car (tire size = 235 / 55R19) having the specifications shown in Table 1 below.

[0144] It has a covering layer, a base layer and an intermediate layer, and has Figure 1 The tread of the structure shown. The overlayer has a loss tangent (LTc) of 0.25 at 30°C. The intermediate layer has a loss tangent (LTm) of 0.15 at 30°C. The ratio of the loss tangent (LTm) to the loss tangent (LTc) is 0.60. The base layer has a loss tangent (LTb) of 0.10 at 30°C.

[0145] In the first tread, the ratio of the thickness TG of the first outer layer to the total thickness TC of the first outer layer thickness TG and the intervening layer thickness TK (TG / TC) is 0.60. The ratio of the total thickness TC to the circumferential groove depth DG (TC / DG) is 0.95. The first tread is engraved with shoulder circumferential grooves, and the ratio of the axial distance WT1 from the reference ground contact edge PH on the first end TE1 side to the boundary PB to the reference ground contact width WH (WT1 / WH) is 65%.

[0146] The ratio (L1 / L2) of the first standard ground contact length L1 to the second standard ground contact length L2 is 0.75. The radius Rc of the center contour line is 700 mm. The terminal portion is provided on the second tread.

[0147] [Comparative Example 1]

[0148] In addition to using Figure 8 A tire of Comparative Example 1 was obtained in the same manner as Example 1, except for the tread structure shown. The tread of Comparative Example 1 includes an overlay layer, an intermediate layer, and a base layer. On the first end TE1 side, a first tread is formed by laminating the overlay layer on the base layer, and on the second end TE2 side, a second tread is formed by laminating the intermediate layer on the base layer.

[0149] The materials of the cover layer and the base layer were the same as those of Example 1. By changing the rubber material, the loss tangent LTm of the intermediate layer was changed, and the ratio (LTm / LTc) was set as shown in Table 1 below.

[0150] A ratio (WT1 / WH) of an axial distance WT1 from the reference ground end PH on the first end TE1 side to the boundary PB to a ground plane width WH of the reference ground plane is 30%.

[0151] The ratio (L1 / L2) of the first standard ground contact length L1 to the second standard ground contact length L2 is 0.50. The radius Rc of the central contour line is 450 mm.

[0152] The ratio of the thickness of the cover layer to the effective groove depth of the circumferential groove is 0.95. The ratio of the thickness of the intermediate layer to the effective groove depth of the circumferential groove is 0.95.

[0153] [Comparative Example 2]

[0154] In addition to using Figure 9 A tire of Comparative Example 2 was obtained in the same manner as Example 1, except for the tread structure shown. The tread of Comparative Example 2 included an overlay layer, an intermediate layer, and a base layer. The materials of the overlay layer, intermediate layer, and base layer were the same as those of Comparative Example 1.

[0155] In Comparative Example 2, the cover layer, the intermediate layer, and the base layer are laminated in the radial direction, and the entire tread is composed of a laminate of these three layers.

[0156] The ratio of the thickness of the cover layer to the total thickness of the cover layer and the intermediate layer is 0.75. This is reported in the "TG / TC" column of Table 1 below. The ratio of the total thickness of the cover layer and the intermediate layer to the effective groove depth of the circumferential groove is 0.95.

[0157] The ratio (L1 / L2) of the first standard ground contact length L1 to the second standard ground contact length L2 is 0.50. The radius Rc of the central contour line is 450 mm.

[0158] [Comparative Examples 3-4]

[0159] A tire of Comparative Example 3-4 was obtained in the same manner as in Example 1 except that the ratio (TG / TC) was as shown in Table 1 below.

[0160] [Examples 2-3]

[0161] A tire of Example 2-3 was obtained in the same manner as in Example 1 except that the radius Rc and the ratio (L1 / L2) were set as shown in Table 2 below.

[0162] [Example 4]

[0163] In addition to setting the terminal configuration to Figure 7 A tire of Example 4 was obtained in the same manner as in Example 1 except for the above-mentioned differences.

[0164] Rolling resistance coefficient (RRC)

[0165] Use rolling resistance tester to measure the rolling resistance coefficient (RRC) of the trial tire when traveling on a drum at a speed of 80 km / h under the following conditions. Its result is shown in the following table 1 with the index of 100 being set to Comparative Example 1. The larger the numerical value, the lower the rolling resistance of the tire. In this evaluation, if the index exceeds 100, it can be judged that it is possible to achieve reduction in rolling resistance.

[0166] Rim: 19×7.5J

[0167] Internal pressure: 210kPa

[0168] Longitudinal load: 6.47kN

[0169] [Wet performance of new tires (WET)]

[0170] The new prototype tire was assembled on a rim (size = 19×7.5J), filled with air, and the internal pressure of the tire was adjusted to 230kPa. The tire was installed on a test vehicle (displacement 2000cm 3 Passenger vehicles). The test vehicles were driven steadily in turns on a test course with a wet surface (water film thickness = 1.4 mm) and their limit speeds were measured. The results are shown in the "WET (NEW)" column in Tables 1 and 2 below, with Comparative Example 1 set to 100. Larger values ​​indicate higher limit speeds and superior wet performance.

[0171] [Changes in wet performance due to wear]

[0172] The new prototype tire was assembled on a rim (size = 19×7.5J), filled with air, and the internal pressure of the tire was adjusted to 230kPa. The tire was installed on a test vehicle (displacement 2000cm 3 Passenger cars). The test vehicle is driven on a test circuit on a dry asphalt road surface to wear out the tire tread. The tread is worn until the groove depth of the circumferential groove reaches 50% of the groove depth of a new tire. Then, on a test circuit on a wet road surface (water film thickness = 1.4 mm), the test vehicle is driven in a stable turn and the limit speed is measured. The change in wetland performance due to wear is evaluated based on the difference between the limit speed obtained in the new state and its limit speed. The results are shown in the "Performance Change" column of the following Tables 1 and 2 as an index set to 100 for Comparative Example 1. The larger the numerical value, the more it can suppress the reduction in wetland performance due to wear.

[0173] [Appearance of worn tires]

[0174] The new prototype tire was assembled on a rim (size = 19×7.5J), filled with air, and the internal pressure of the tire was adjusted to 230kPa. The tire was installed on a test vehicle (displacement 2000cm 3Passenger vehicles were driven on a dry asphalt test track to wear the tire tread. The tread was worn until the circumferential groove depth reached 50% of the groove depth of a new tire. The tread wear was then visually inspected. The results are presented as an index in the "Appearance" column of Tables 1 and 2 below. A larger value indicates a better worn appearance. This evaluation was performed for Examples 1 and 4.

[0175]

Table 1

[0176]

[0177]

Table 2

[0178]

[0179] As shown in Table 1-2, the examples were able to prevent a significant decrease in wet performance due to wear and achieve a reduction in rolling resistance. This evaluation result clearly demonstrates the superiority of the present invention.

[0180] Industrial Applicability

[0181] The above-described technology for preventing a significant decrease in wet performance due to wear and achieving a reduction in rolling resistance can also be applied to various tires.

[0182]

Number Description

[0183] 2. 72… tires;

[0184] 4…tread;

[0185] 6…sidewall;

[0186] 24, 24s, 24m…circumferential groove;

[0187] 26, 26s, 26m, 26c…Land Department;

[0188] 44…covering layer;

[0189] 46…middle layer;

[0190] 48… Grassroots;

[0191] 50…first tread;

[0192] 52…Second tread;

[0193] 54…first outer layer;

[0194] 56…intervention layer;

[0195] 58…first inner layer;

[0196] 60…second outer layer;

[0197] 62…Second inner layer;

[0198] 64…Terminal portion.

Claims

1. A tire having a tread that contacts a road surface. The tread comprises an overlay layer, an intermediate layer having a loss tangent at 30°C lower than that of the overlay layer, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer. specifies the orientation of the tread relative to the vehicle, Of the two ends of the tread, the end disposed on the outer side in the width direction of the vehicle is a first end, and the end disposed on the inner side is a second end. The tread is composed of a first tread located on the first end side and a second tread located on the second end side. The first tread includes a first outer layer, an intervening layer located radially inward of the first outer layer, and a first inner layer located radially inward of the intervening layer. The second tread includes a second outer layer and a second inner layer located radially inward of the second outer layer. The first outer layer is formed by the cover layer, The intervening layer and the second outer layer are formed by the intermediate layer, The first inner layer and the second inner layer are formed by the base layer, In the first tread, a ratio of the thickness of the first outer layer to the total thickness of the first outer layer and the thickness of the intervening layer is 0.50 or more and 0.70 or less.

2. The tire according to claim 1, wherein The tread is engraved with at least three circumferential grooves arranged in parallel in the axial direction. Among the at least three circumferential grooves, the circumferential groove located on the outer side in the axial direction is a shoulder circumferential groove, and the first tread is engraved with the shoulder circumferential groove.

3. The tire according to claim 1 or 2, wherein: A ratio of the loss tangent of the intermediate layer at 30° C. to the loss tangent of the cover layer at 30° C. is 0.50 or more and 0.70 or less.

4. The tire according to any one of claims 1 to 3, wherein The tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and the camber angle of the tire is set to -1°. A load of 70% of the regular load is applied to the tire as a longitudinal load. The contact patch obtained by the tire contacting a flat road surface is referred to as the standard contact patch. The grounding length measured at a position corresponding to 80% of the grounding width of the standard grounding plane is the standard grounding length. The standard grounding length on the first end side is a first standard grounding length, the standard grounding length on the second end side is a second standard grounding length, and a ratio of the first standard grounding length to the second standard grounding length is greater than or equal to 0.60 and less than or equal to 0.

90.

5. The tire according to any one of claims 1 to 4, wherein The tire is assembled onto a regular rim and the internal pressure of the tire is adjusted to 230 kPa. In a meridian cross-section of the tire in an unloaded state, the outer surface of the tire includes a tread surface and a pair of side surfaces connected to one end of the tread surface. The profile of the tread surface includes a curved contour line formed by a circular arc passing through the equator of the tire, The radius of the curved contour line is greater than or equal to 500 mm and less than or equal to 1000 mm.

6. The tire according to any one of claims 1 to 5, wherein: The first tread includes a terminal portion that penetrates the intervening layer and the first inner layer. The terminal portion has conductivity.

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