Tire

Abstract

A tire (2) according to the present application can reduce the rolling resistance without reducing the WET performance. The tire (2) includes a tread (4) and a belt layer (14). The belt layer (14) includes an inner layer (38) and an outer layer (40). An end portion of the outer layer (40) is located axially inward of an end portion of the inner layer (38). A circumferential fine groove (48) extending continuously in the circumferential direction is formed in a shoulder land portion (46s). A groove width of the circumferential fine groove (48) is narrower than a groove width of a shoulder circumferential groove (44s). The circumferential fine groove (48) is located axially between the shoulder circumferential groove (44s) and the end portion of the outer layer (40). A ratio of an axial distance from the shoulder circumferential groove (44s) to the circumferential fine groove (48) to an axial distance from the shoulder circumferential groove (44s) to the end portion of the outer layer (40) is 15% or more and 55% or less.

Description

Technical Field

[0001] The present invention relates to a tire, and more particularly to a tire mounted on a passenger vehicle. Background Art

[0002] Due to environmental concerns, tires installed on vehicles are required to have reduced rolling resistance. Consequently, research is underway to reduce the number of components that make up a tire, reduce the thickness of these components, and employ low-heat-generating materials for these components (e.g., Patent Document 1 below).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-120242

[0004] The tread consists of a crown and a base. The crown has the tread surface that contacts the road surface. Generally, the crown prioritizes grip over heat generation.

[0005] Using a low-heat-generating cross-linked rubber in the base and the crown with a cross-linked rubber designed for low heat generation reduces the tire's rolling resistance. However, this reduces the grip performance on wet roads (hereinafter referred to as "WET performance").

[0006] Tires are required to have low rolling resistance and good WET performance. There is a need to establish a technology that can reduce rolling resistance without compromising WET performance.

[0007] By creating fine grooves in the shoulder land portion, the strain generated therein is reduced. This is expected to reduce rolling resistance without changing WET performance. However, depending on the groove location, damage such as belt end delamination (BEL) may occur. Therefore, it is difficult to say that rolling resistance has been reduced. Summary of the Invention

[0008] 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 reducing rolling resistance without degrading WET performance.

[0009] The tire of one embodiment of the present application includes a tread that grounds against a road surface, and a belt layer located on the radially inner side of the tread. A plurality of circumferential grooves are engraved in the tread in a row along the axial direction, and at least three land portions are formed in the tread. The circumferential groove located on the axially outermost side among the plurality of circumferential grooves is a shoulder circumferential groove, and the land portion located on the axially outermost side among the at least three land portions is a shoulder land portion. The belt layer includes an inner layer and an outer layer located on the radially outer side of the inner layer. The end portion of the outer layer is located on the axially inner side of the end portion of the inner layer. A circumferential fine groove that extends continuously in the circumferential direction is engraved in the shoulder land portion. The groove width of the circumferential fine groove is narrower than the groove width of the shoulder circumferential groove. The circumferential fine groove is located between the shoulder circumferential groove and the end portion of the outer layer in the axial direction. The ratio of the axial distance from the shoulder circumferential groove to the circumferential fine groove to the axial distance from the shoulder circumferential groove to the end portion of the outer layer is 15% or more and 55% or less.

[0010] Preferably, in the tire, the ratio of the groove width of the circumferential fine groove to the width of the tread is 1.0% or more and 2.5% or less.

[0011] Preferably, in the tire, the ratio of the groove depth of the circumferential fine groove to the thickness of the tread is 20% or more and 95% or less.

[0012] Preferably, in the tire, the tread includes a crown top portion that grounds against the road surface, and a base portion located on the radially inner side of the crown top portion, the loss tangent of the base portion at 30°C is lower than the loss tangent of the crown top portion at 30°C, and the base portion is located on the radially inner side of the circumferential fine groove.

[0013] Preferably, in the tire, the groove bottom of the circumferential fine groove is constituted by the base portion.

[0014] Preferably, in the tire, the end portion of the base portion is located on the axially inner side of the end portion of the inner layer.

[0015] Preferably, in the tire, the ratio of the axial width of the base portion to the axial width of the outer layer is 95% or more and 105% or less.

[0016] According to the present application, a tire that does not reduce WET performance and enables reduction in rolling resistance can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a cross-sectional view showing a portion of a tire of one embodiment of the present application.

[0018] Figure 2 is a cross-sectional view showing a shoulder land portion.

[0019] Figure 3 It is a cross-sectional view showing a circumferential fine groove.

[0020] Figure 4 It is a cross-sectional view showing a part of the tread portion.

[0021] Explanation of the reference numerals: 2...tire; 4...tread; 6...sidewall; 10...bead; 12...carcass; 14...belt; 16...belt; 24...tread surface; 28...crown top; 30...base; 38...inner layer; 40...outer layer; 44, 44s, 44m...circumferential groove; 46, 46s, 46m, 46c...land portion; 48...circumferential fine groove. DETAILED DESCRIPTION

[0022] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0023] In the present disclosure, a state in which a tire is assembled on a regular rim, the internal pressure of the tire is adjusted to a regular internal pressure, and no load is applied to the tire is referred to as a regular state.

[0024] In this disclosure, unless otherwise specified, the dimensions and angles of various parts of the tire are measured under normal conditions.

[0025] The dimensions and angles of various parts in the meridian cross-section of the tire, which cannot be measured when the tire is assembled on a regular rim, are measured by making the distance between the left and right beads consistent with the distance between the beads in the tire assembled on a regular rim in the cross-section of the tire obtained by cutting the tire along a plane including the rotation axis (hereinafter referred to as the reference cut surface).

[0026] A standard rim is a rim specified in the tire's standards. Standard rims in the JATMA standard, Design rims in the TRA standard, and Measuring rims in the ETRTO standard are standard rims.

[0027] The normal internal pressure refers to the internal pressure specified in the tire's standards. These include the "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLDINFLATION PRESSURES" section of the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard.

[0028] The "normal load" refers to the load specified in the tire's standards. Examples include the "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" section of the TRA standard, and the "LOADCAPACITY" in the ETRTO standard.

[0029] In the present disclosure, the loss tangent (tan δ) of the crosslinked rubber component among the components constituting the tire at a temperature of 30°C is measured under the following conditions using a viscoelastic spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) in accordance with JIS K6394.

[0030] Initial strain = 10%

[0031] Dynamic strain = 2%

[0032] Frequency = 10 Hz

[0033] Deformation Mode = Stretch

[0034] In this measurement, the test piece is sampled from the tire. If it is not possible to sample the test piece from the tire, the test piece is sampled from a sheet of cross-linked rubber (hereinafter referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at 170°C for 12 minutes.

[0035] In this disclosure, the tread portion of a tire refers to the portion of the tire that contacts the road surface. The bead portion refers to the portion of the tire that engages the wheel rim. The side portion refers to the portion of the tire that spans between the tread and bead portions. A tire includes a tread portion, a pair of bead portions, and a pair of side portions.

[0036] Figure 1 A portion of a tire 2 according to one embodiment of the present invention is shown. The tire 2 is a pneumatic tire for passenger cars.

[0037] Figure 1 A portion of a cross section of the tire 2 (hereinafter referred to as a meridian cross section) taken along a plane including the rotation axis of the tire 2 is shown. Figure 1 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 1 The direction perpendicular to the paper surface is the circumferential direction of the tire 2. The dot-dash line CL represents the equatorial plane of the tire 2.

[0038] The tire 2 is assembled to the rim R. The rim R is a regular rim. Air is filled inside the tire 2 to adjust the internal pressure of the tire 2. The tire 2 assembled to the rim R is also called a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 assembled to the rim R.

[0039] exist Figure 1 The position indicated by the reference symbol PC in FIG. 1 is the intersection of the outer surface of the tire 2 and the equatorial plane CL. Intersection PC is also referred to as the equator of the tire 2. When the grooves are located on the equatorial plane, the equator PC is determined based on a hypothetical outer surface (the hypothetical tread surface described later) obtained by assuming the absence of grooves. The equator PC is also the radially outer end of the tire 2.

[0040] exist Figure 1 The position indicated by reference symbol PW in FIG is the axial outer end of the tire 2. When decorations such as patterns and characters are located on the outer surface, the outer end PW is determined based on a virtual outer surface assuming that there is no decoration.

[0041] exist Figure 1 The length denoted by the reference symbol WA is the cross-sectional width of the tire 2 (see JATMA, etc.). The cross-sectional width WA is the axial distance from the first outer end PW to the second outer end PW. The cross-sectional width WA is the maximum width of the tire 2, with the outer end PW being the position where the tire 2 exhibits the maximum width WA (hereinafter referred to as the maximum width position). The cross-sectional width WA is determined for the tire 2 in a normal condition.

[0042] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of bead portions 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a belt 16 , an inner liner 18 , a pair of breaker layers 20 , and a pair of insulation layers 22 as elements.

[0043] The tread 4 contacts the road surface at a tread surface 24. The tread 4 has a tread surface 24 that contacts the road surface.

[0044] On the outer surface of the tire 2 , the side surfaces 26 are connected to the tread surface 24 . The outer surface of the tire 2 includes the tread surface 24 and a pair of side surfaces 26 .

[0045] In a meridian cross section, the profile of the tread surface 24 includes a plurality of arcs arranged in the axial direction. The arc located axially outward among the plurality of arcs is a shoulder arc having the smallest radius Rs. The contour line of the side surface 26 is connected to the shoulder arc.

[0046] The position indicated by reference symbol PT is the boundary between the shoulder arc and the arc located next to the shoulder arc. The straight line LT is a tangent line to the shoulder arc at the boundary PT.

[0047] The position indicated by reference symbol PS is the boundary between the shoulder arc and the contour line of the side surface 26. The straight line LS is a tangent line to the shoulder arc at the boundary PS.

[0048] Reference symbol TE is the intersection of tangent line LT and tangent line LS. In the present disclosure, this intersection TE is the reference end of the tread 4. The length denoted by reference symbol WT is the axial distance from the first reference end TE to the second reference end TE. In the present disclosure, the axial distance WT is the width of the tread 4.

[0049] In the tire 2 , a ratio (WT / WA) of the width WT of the tread 4 to the cross-sectional width WA of the tire 2 is 75% or more and 90% or less.

[0050] The tread 4 includes a crown portion 28 and a base portion 30 .

[0051] The crown 28 includes the tread surface 24. The crown 28 contacts the road surface. The crown 28 is made of a cross-linked rubber that takes wear resistance and grip performance into consideration.

[0052] The base portion 30 is located radially inward of the crown 28. The end 30e of the base portion 30 is located axially inward of the end 28e of the crown 28. The entire base portion 30 is covered by the crown 28. Unless the tread 4 wears and exposes the base portion 30, the base portion 30 does not contact the road surface. Unlike the crown 28, the base portion 30 is not designed with considerations for wear resistance and grip performance.

[0053] The base portion 30 is made of a cross-linked rubber with low heat buildup. The loss tangent of the base portion 30 at 30°C (hereinafter referred to as the loss tangent of the base portion 30, LTb) is lower than the loss tangent of the crown 28 at 30°C (hereinafter referred to as the loss tangent of the crown 28, LTc). Specifically, the ratio of the loss tangent of the base portion 30, LTb, to the loss tangent of the crown 28, LTc (LTb / LTc), is preferably 0.15 or greater and preferably 0.55 or less.

[0054] In this tire 2, the loss tangent Ltb of the base portion 30 is preferably 0.11 or less. The base portion 30 contributes to reducing rolling resistance. From this perspective, the lower the loss tangent Ltb, the better, so no preferred lower limit is set.

[0055] In the tire 2 , in its meridian cross section, the base portion 30 is configured to have a uniform thickness in the center portion and to gradually become thinner toward the end portions in the axially outer portion.

[0056] For example, the ratio of the thickness of the base portion 30 measured along the equatorial plane to the thickness of the tread 4 is set within a range of 10% to 80%. When emphasis is placed on rolling resistance, the tread 4 is constructed with a thicker base portion 30. When emphasis is placed on grip performance, the tread 4 is constructed with a thinner base portion 30.

[0057] Each sidewall 6 is connected to an end portion of the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 is made of a cross-linked rubber in consideration of cut resistance.

[0058] Each bead portion 8 is located radially inward of the sidewall 6. The bead portion 8 is in contact with the rim R. The bead portion 8 is made of a cross-linked rubber in consideration of wear resistance.

[0059] Each bead 10 is located axially inward of the bead portion 8. The bead 10 is located radially inward of the sidewall 6.

[0060] The tire bead 10 includes a core 32 and an apex 34. The core 32 extends circumferentially. Although not shown, the core 32 is made of a steel wire rod. The apex 34 is located radially outward from the core 32. The apex 34 tapers radially outward. The apex 34 is made of highly rigid cross-linked rubber.

[0061] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of bead portions 8. The carcass 12 is mounted between the first bead 10 and the second bead 10 of the pair of beads 10. The carcass 12 includes at least one carcass ply 36.

[0062] To reduce rolling resistance, the carcass 12 of this tire 2 is constructed from a single carcass ply 36. Although not shown, the carcass ply 36 includes a plurality of aligned carcass cords. These carcass cords intersect the equatorial plane. The carcass 12 of this tire 2 has a radial construction. In this tire 2, cords composed of organic fibers are used as the carcass cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0063] The carcass ply 36 includes a ply main body 36a and a pair of first folded portions 36b. The ply main body 36a is laid between the first and second beads 10. Each folded portion 36b is connected to the ply main body 36a and folded axially from the inside to the outside at each bead 10.

[0064] The belt layer 14 is located radially inward of the tread 4 . The belt layer 14 is laminated on the carcass 12 .

[0065] exist Figure 1 The length denoted by reference symbol WR in FIG. 1 is the axial width of the belt layer 14. The axial width WR is the axial distance from the first end to the second end of the belt layer 14. The equatorial plane intersects the belt layer 14 at the center of the axial width WR of the belt layer 14.

[0066] In the tire 2 , the axial width WR of the belt layer 14 is equal to or greater than 85% and equal to or less than 100% of the width WT of the tread 4 .

[0067] The belt layer 14 includes an inner layer 38 and an outer layer 40. The inner layer 38 is located radially outward of the carcass body 36a and laminated thereto. The outer layer 40 is located radially outward of the inner layer 38 and laminated thereto.

[0068] In the tire 2 , one or more layers may be provided between the inner layer 38 and the outer layer 40 . The belt 14 is preferably composed of two layers, the inner layer 38 and the outer layer 40 , from the viewpoint of weight reduction.

[0069] like Figure 1 As shown, the end 40e of the outer layer 40 is located axially inward of the end 38e of the inner layer 38. The outer layer 40 is narrower than the inner layer 38. The length from the end 40e of the outer layer 40 to the end 38e of the inner layer 38 is 3 mm or more and 10 mm or less. The axial width WR of the belt layer 14 described above is represented by the axial width of the wider inner layer 38.

[0070] Although not shown in the figure, the inner layer 38 and the outer layer 40 each include a plurality of arranged belt cords. These belt cords are covered with rubber. Each belt cord is inclined relative to the equatorial plane. The angle formed by the belt cords relative to the equatorial plane (the inclination angle of the belt cords) is greater than 10 degrees and less than 35 degrees. The inclination direction of the belt cords (inner belt cords) contained in the inner layer 38 is opposite to the inclination direction of the belt cords (outer belt cords) contained in the outer layer 40. The inclination angle of the inner belt cords is the same as the inclination angle of the outer belt cords. The material of the belt cords is steel.

[0071] The belt 16 is located between the tread 4 and the belt layer 14 in the radial direction. The belt 16 is laminated on the belt layer 14.

[0072] Although not shown, the belt 16 includes a helically wound belt cord. The belt cord is covered with a rubber coating. The belt cord substantially extends in the circumferential direction. Specifically, the angle formed by the belt cord with respect to the circumferential direction is 5° or less. The belt 16 has an endless structure. The belt cord is made of an organic fiber. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0073] In the axial direction, the end 16e of the band 16 is located outside the end 14e of the belt 14. The length from the end 14e of the belt 14 to the end 16e of the band 16 is 3 mm to 7 mm. The band 16 binds the end 14e of the belt 14.

[0074] The belt 16 of this tire 2 is a full belt. The full belt has two ends facing each other across the equatorial plane. The belt 16 covers the entire belt layer 14. The belt 16 constrains the entire belt layer 14. In this tire 2, changes in the shape of the ground contact patch can be suppressed.

[0075] The belt 16 may also be a pair of edge belts that are arranged axially apart across the equatorial plane and cover portions of the end portions 14e of the belt layer 14. In this case, the belt 16 contributes to lightweighting of the tire 2. To increase the rigidity of the tread 4, the belt 16 is composed of a full belt and a pair of edge belts.

[0076] The inner liner 18 is located inside the carcass 12. The inner liner 18 forms the inner surface of the tire 2. The inner liner 18 is made of a cross-linked rubber having excellent air barrier properties. The inner liner 18 maintains the internal pressure of the tire 2.

[0077] The buffer layers 20 are arranged axially apart. They are located between the ends of the belt 14 and the band 16 and the carcass 12. The buffer layers 20 are made of a cross-linked rubber having low rigidity. The buffer layers 20 are not essential elements of the tire 2. Depending on the specifications of the tire 2, the buffer layers 20 may not be provided.

[0078] Each insulation layer 22 is positioned between the carcass 12 and the inner liner 18. A first end 22ea of ​​the insulation layer 22 is positioned axially inward of the end 14e of the belt 14. A second end 22eb of the insulation layer 22 is positioned radially inward of the maximum width position PW. The second end 22eb of the insulation layer 22 is positioned radially outward of the tire bead 10. The insulation layer 22 is formed of a cross-linked rubber that takes adhesive properties into consideration.

[0079] In the tire 2, in the portion where the insulation layer 22 is provided, the inner liner 18 is bonded to the carcass 12 via the insulation layer 22. In the portion where the insulation layer 22 is not provided, such as the portion between the first end 22ea of ​​the first insulation layer 22 and the first end 22ea of ​​the second insulation layer 22 (not shown), and the portion inside from the second end 22eb of the insulation layer 22, the inner liner 18 is directly bonded to the carcass 12. The entire inner liner 18 may also be bonded to the carcass 12 via the insulation layer 22. From the viewpoint of reducing rolling resistance, such as Figure 1 As shown, it is preferable to provide a pair of separators 22 that are spaced apart in the axial direction, and each separator 22 is arranged in a region between the end portion 14e of the belt layer 14 and the maximum width position PW.

[0080] Grooves 42 are formed on the tread 4 of the tire 2, thereby forming a tread pattern.

[0081] The grooves 42 include circumferential grooves 44 that extend continuously in the circumferential direction. In the tire 2, a plurality of circumferential grooves 44 arranged in the axial direction are engraved on the tread 4. Figure 1 In the tire 2 shown, four circumferential grooves 44 are engraved on the tread 4 .

[0082] Of the four circumferential grooves 44, the circumferential groove 44 located most axially outward is the shoulder circumferential groove 44s, and the circumferential groove 44 located axially inward of the shoulder circumferential groove 44s is the middle circumferential groove 44m.

[0083] The tread 4 of the tire 2 is provided with a pair of middle circumferential grooves 44 m and a pair of shoulder circumferential grooves 44 s .

[0084] exist Figure 1 In the figure, the two-dot chain line LV represents an imaginary tread surface assuming that the tread 4 does not have the groove 42. The length indicated by the reference symbol d is the distance from the imaginary tread surface LV to the bottom of the circumferential groove 44. Distance d is the groove depth of the circumferential groove 44. The length indicated by the reference symbol w is the groove width of the circumferential groove 44. The groove width w represents the opening width of the circumferential groove 44 in the tread surface 24.

[0085] The groove depth d of the circumferential groove 44 is preferably 70% to 95% of the thickness of the tread 4. The thickness of the tread 4 used to determine the groove depth d is represented by the distance from the imaginary tread surface LV to the inner surface of the tread 4 measured along the line segment representing the groove depth d.

[0086] The groove width w of the circumferential groove 44 is preferably not less than 3% and not more than 15% of the width WT of the tread 4 .

[0087] As described above, in the tire 2, a plurality of circumferential grooves 44 arranged in the axial direction are engraved on the tread 4. Thus, at least three land portions 46 are formed on the tread 4. Figure 1 As shown, the tread 4 of the tire 2 is formed with five land portions 46 . The land surfaces of these land portions 46 are included in the tread surface 24 .

[0088] Of the five land portions 46, the axially outermost land portion 46 is a shoulder land portion 46s. The land portion 46 axially inward of the shoulder land portion 46s is a middle land portion 46m. The land portion 46 axially inward of the middle land portion 46m, i.e., the central land portion 46 of the five axially arranged land portions 46, is a central land portion 46c. In this tire 2, the central land portion 46c includes the equator PC.

[0089] The tread 4 of the tire 2 is formed with a center land portion 46 c , a pair of middle land portions 46 m , and a pair of shoulder land portions 46 s .

[0090] The axial width of the shoulder land portion 46 s is represented by the axial distance from the boundary between the shoulder circumferential groove 44 s and the land surface of the shoulder land portion 46 s to the end TE of the tread 4 .

[0091] In the tire 2 , the ratio of the axial width of the shoulder land portion 46 s to the width WT of the tread 4 is preferably 15% or more and 30% or less.

[0092] Like the central land portion 46c and the intermediate land portion 46m, the axial width of the land portion 46 located between the two circumferential grooves 44 is represented by the axial width of the land surface. This axial width is appropriately determined in consideration of the number of circumferential grooves 44 formed in the tread 4, the groove width w, and the like.

[0093] The tread 4 of the tire 2 repeatedly engages and disengages from the road surface. In the disengaged state, the land surface of the shoulder land portions 46s is located radially inward of the land surface of the center land portion 46c. In the engaged state, the tread 4 presses against the road surface. This causes the tread 4 to deform. The center land portion 46c moves radially inward, expanding the contact patch axially outward from the equator PC. The shoulder land portions 46s then make contact. In the engaged state, the tread 4 deforms, causing the tread surface 24 to warp in the opposite direction. Consequently, compressive strain occurs in the shoulder land portions 46s.

[0094] Since compressive strain is a factor that increases rolling resistance, the inventors conducted a detailed investigation into the generation behavior of compressive strain and found that even if particularly large compressive strain is generated near the end 40e of the outer layer 40 in the shoulder land portion 46s, the generation of compressive strain can be effectively suppressed by engraving circumferential fine grooves having a groove width narrower than the groove width w of the circumferential groove 44 in a specific area of ​​the portion between the shoulder circumferential groove 44s and the end 40e of the outer layer 40, thereby completing the present invention.

[0095] Figure 2 express Figure 1 A portion of a tire 2 is shown. Figure 2 The shoulder land portion 46s of the tread portion is shown.

[0096] The shoulder land portion 46s of the tire 2 is provided with a circumferential narrow groove 48. The circumferential narrow groove 48 forms part of the groove 42 that constitutes the tread pattern. The circumferential narrow groove 48 extends continuously in the circumferential direction. The circumferential narrow groove 48 divides the shoulder land portion 46s into an inner land portion 50 and an outer land portion 52.

[0097] like Figure 2 As shown, the circumferential narrow groove 48 is axially located between the shoulder circumferential groove 44s and the end 40e of the outer layer 40. The groove width of the circumferential narrow groove 48 is narrower than the groove width w of the shoulder circumferential groove 44s. Therefore, the circumferential narrow groove 48 has a minimal effect on the rigidity of the shoulder land portion 46s. The shoulder land portion 46s has the necessary rigidity. In this tire 2, a decrease in cornering performance can be suppressed.

[0098] exist Figure 2 The length indicated by reference numeral DY is an axial distance from the shoulder circumferential groove 44s to the end portion 40e of the outer side layer 40. The length indicated by reference numeral DX is an axial distance from the shoulder circumferential groove 44s to the circumferential fine groove 48. The axial distance DX is an axial width of the land surface of the inner side land portion 50.

[0099] As described above, in this tire 2, the circumferential fine groove 48 is located in the axial direction between the shoulder circumferential groove 44s and the end portion 40e of the outer side layer 40. In particular, in this tire 2, the ratio (DX / DY) of the axial distance DX from the shoulder circumferential groove 44s to the circumferential fine groove 48 to the axial distance DY from the shoulder circumferential groove 44s to the end portion 40e of the outer side layer 40 is 15% or more and 55% or less.

[0100] Since the ratio (DX / DY) is 15% or more, the circumferential fine groove 48 and the shoulder circumferential groove 44s can be inhibited from interfering with each other. Since the inner side land portion 50 has necessary rigidity, the circumferential fine groove 48 contributes to the suppression of the generation of compression strain. Since the generation of compression strain is suppressed, reduction of the rolling resistance is achieved in this tire 2. From this viewpoint, the ratio (DX / DY) is preferably 25% or more, more preferably 35% or more, and further preferably 45% or more.

[0101] Since the ratio (DX / DY) is 55% or less, the circumferential fine groove 48 is disposed at an appropriate distance from the end portion 40e of the outer side layer 40. The circumferential fine groove 48 and the end portion 40e of the outer side layer 40 can be inhibited from interfering with each other. Damage such as delamination can be inhibited from occurring at the portion of the end portion 40e of the outer side layer 40. Even in this case, the circumferential fine groove 48 can stably and sufficiently function to suppress the generation of compression strain. Since the generation of compression strain can be suppressed, reduction of the rolling resistance is achieved in this tire 2. From this viewpoint, the ratio (DX / DY) is more preferably 50% or less.

[0102] In this tire 2, even in the shoulder land portion 46s, the circumferential fine groove 48 having a groove width narrower than that of the shoulder circumferential groove 44s is formed in a specific region of the portion between the shoulder circumferential groove 44s and the end portion 40e of the outer side layer 40. Thus, the generation of compression strain can be suppressed, and reduction of the rolling resistance is achieved.

[0103] In this tire 2, it is not necessary to consider low heat generation property for the crosslinked rubber constituting the crown top portion 28 in order to reduce the rolling resistance. This tire 2 can be configured such that the crown top portion 28 is constituted by crosslinked rubber that places importance on the grip performance on a WET road surface (hereinafter, referred to as WET performance).

[0104] This tire 2 can achieve reduction of the rolling resistance without lowering the WET performance.

[0105] ​ Figure 3 indicates a portion of the shoulder land portion 46s. Figure 2 indicates a portion provided with the circumferential sipe 48. Figure 3 indicates a portion provided with the circumferential sipe 48.

[0106] In Figure 3 the length indicated by reference sign WG is a groove width of the circumferential sipe 48. The groove width WG is indicated by an opening width of the circumferential sipe 48 in the tread surface 24. This groove width WG is determined in the tire 2 in the normal state.

[0107] The length indicated by reference sign a is a groove depth of the circumferential sipe 48. The groove depth a is a distance from the imaginary tread surface LV to a groove bottom of the circumferential sipe 48.

[0108] The length indicated by reference sign b is a thickness of the tread 4. This thickness b is indicated by a distance from the imaginary tread surface LV to an inner surface of the tread 4 measured along the line segment indicating the groove depth a.

[0109] In the case where the groove depth a of the circumferential sipe 48 and the thickness b of the tread 4 are measured in the reference cross section described above, a straight line connecting both edges of the circumferential sipe 48 is used as the imaginary tread surface LV.

[0110] As described above, in this tire 2, the groove width WG of the circumferential sipe 48 is narrower than the groove width ws of the shoulder circumferential groove 44s. The narrower the groove width WG, the less the circumferential sipe 48 affects the rigidity of the shoulder land portion 46s. However, if the groove width WG is less than 1% of the width WT of the tread 4, the circumferential sipe 48 is closer to a knife slot than to a groove, the groove walls are close to each other due to the effect of load, and the circumferential sipe 48 can not function as a groove. In this case, it can be impossible to sufficiently suppress the generation of compression strain.

[0111] In this tire 2, it is preferable that the ratio (WG / WT) of the groove width WG of the circumferential sipe 48 to the width WT of the tread 4 be 1.0% or more. Thereby, it is possible to effectively contribute to the circumferential sipe 48 suppressing the generation of compression strain. Since it is possible to suppress the generation of compression strain, in this tire 2, reduction of rolling resistance is achieved. From this viewpoint, the ratio (WG / WT) is more preferably 1.5% or more.

[0112] The ratio (WG / WT) is preferably 2.5% or less. Thereby, it is possible to suppress the influence of the circumferential sipe 48 on the rigidity of the shoulder land portion 46s. In this tire 2, good handling stability is maintained. From this viewpoint, the ratio (WG / WT) is more preferably 2.0% or less.

[0113] Even when the ratio (WG / WT) is 1.0% or greater, the groove width WG may be less than 1.1 mm. In this case, the circumferential narrow groove 48 approaches a sipe and may not function to suppress the generation of compressive strain. To ensure the function of suppressing the generation of compressive strain, the groove width WG of the circumferential narrow groove 48 is preferably greater than 1.1 mm. This groove width WG is more preferably 1.2 mm or greater, even more preferably 1.5 mm or greater, and particularly preferably 1.6 mm or greater.

[0114] In the tire 2 , the ratio (α / β) of the groove depth α of the circumferential narrow groove 48 to the thickness β of the tread 4 is preferably 20% or more and 95% or less.

[0115] Setting the ratio (α / β) to 20% or greater effectively contributes to suppressing the generation of compressive strain in the circumferential fine groove 48. This suppression of compressive strain reduces rolling resistance in the tire 2. From this perspective, the ratio (α / β) is more preferably 50% or greater, and even more preferably 80% or greater.

[0116] By setting the ratio (α / β) to 95% or less, the bottom of the circumferential narrow groove 48 is positioned at an appropriate distance from the belt 16. This tire 2 can prevent appearance defects caused by the bottom of the circumferential narrow groove 48 approaching the belt 16. From this perspective, the ratio (α / β) is more preferably 90% or less.

[0117] When the shoulder land portion 46s presses against the road surface, strain is generated at the bottom of the circumferential narrow groove 48. This strain may contribute to an increase in rolling resistance. In this case, the effect of reducing rolling resistance by suppressing the generation of compressive strain in the circumferential narrow groove 48 is partially offset by the strain generated at the groove bottom.

[0118] In the tire 2, as Figure 3 As shown, the base 30 is located radially inward of the circumferential groove 48. Figure 3 In the illustrated circumferential narrow groove 48, the groove bottom is provided at the base portion 30. In other words, the base portion 30 constitutes the groove bottom of the circumferential narrow groove 48. As described above, the loss tangent LTb of the base portion 30 is lower than the loss tangent LTc of the crown 28.

[0119] In this tire 2, the base portion 30 located radially inward of the circumferential narrow groove 48 suppresses heat generation caused by strain generated at the groove bottom of the circumferential narrow groove 48. This tire 2 can fully utilize the rolling resistance reduction effect brought about by the function of the circumferential narrow groove 48 to suppress the generation of compressive strain.

[0120] A crown top 28 may be arranged between the circumferential groove 48 and the base 30. However, from the viewpoint of effectively suppressing heat generation caused by strain generated at the groove bottom of the circumferential groove 48, as shown in FIG. Figure 3 As shown, it is more preferable that the groove bottom of the circumferential narrow groove 48 is formed by the base portion 30 .

[0121] Figure 4 express Figure 1 A portion of a tire 2 is shown. Figure 4 Indicates a part of the tread. Figure 4 As shown, the end 30e of the base 30 is located axially inward of the end 38e of the inner layer 38. The position of the end 30e of the base 30 is substantially consistent with the position of the end 40e of the outer layer 40 in the axial direction.

[0122] exist Figure 4 The length indicated by the reference symbol WB is the axial width of the base portion 30. This axial width WB is the axial distance from the first end 30e to the second end 30e of the base portion 30. The length indicated by the reference symbol WS is the axial width of the outer layer 40. This axial width WS is the axial distance from the first end 40e to the second end 40e of the outer layer 40.

[0123] In a running tire, the shoulder land portion moves actively. Consequently, various strains occur in this area, contributing to increased rolling resistance. Strain generated at the ends of the belt layer also contributes to damage such as belt end delamination (BEL).

[0124] In order to ensure the volume of the base composed of low-heat-generating cross-linked rubber and reduce rolling resistance, in previous tires, the end of the base is arranged axially outside the end of the belt, and the tread is formed in a manner such that the base covers the belt layer and the entire belt.

[0125] However, low-heat-generating cross-linked rubber has low strength. Therefore, conventional treads with the aforementioned structure inevitably carry the risk of damage, such as BEL. To ensure that tires continue to consistently achieve the effect of reducing rolling resistance, it is necessary to establish technologies that reduce the risk of damage.

[0126] In this tire 2, by engraving circumferential grooves 48 in specific areas of the shoulder land portion 46s, the generation of compressive strain, which increases rolling resistance, can be suppressed. Therefore, even if the tread 4 is constructed such that the end 30e of the base portion 30 is located axially inward of the end 38e of the inner layer 38, the rolling resistance of the tire 2 can be reduced. Because the crown 28 can constitute the entire tread 4, partially covering the end of the belt layer 14, the risk of damage such as BEL is reduced. This tire 2 can stably and continuously achieve the effect of reducing rolling resistance. This tire 2 contributes to improving the fuel economy of the vehicle. Because the crown 28 can be constructed from a cross-linked rubber that emphasizes WET performance, this tire 2 can also continuously achieve good WET performance. From this perspective, in this tire 2, the end 30e of the base portion 30 is preferably located axially inward of the end 38e of the inner layer 38.

[0127] From the perspective of reducing the risk of damage, the position of the end 30e of the base portion 30 is preferably substantially aligned in the axial direction with the position of the end 40e of the outer layer 40. Specifically, the ratio of the axial width WB of the base portion 30 to the axial width WS of the outer layer 40 (WB / WS) is preferably 95% or more and 105% or less.

[0128] By setting the ratio (WB / WS) to 95% or more, the volume occupied by the base portion 30 in the tread 4 increases. This tread 4 can contribute to reducing rolling resistance. From this viewpoint, the ratio (WB / WS) is more preferably 98% or more.

[0129] By setting the ratio (WB / WS) to 105% or less, the base portion 30 is positioned sufficiently apart from the ends of the belt layer 14 and the band 16. This placement of the base portion 30 helps reduce the risk of damage. From this perspective, the (WB / WS) is more preferably 102% or less.

[0130] As described above, the present invention provides a tire 2 capable of reducing rolling resistance without compromising WET performance. In particular, the present invention exhibits significant effects in a passenger car tire 2 in which the ratio of the axial width of the shoulder land portion 46s to the width WT of the tread 4 is 15% or more and 30% or less.

[0131] Example

[0132] Hereinafter, the present invention will be described in further detail with reference to Examples and the like, but the present invention is not limited to the Examples.

[0133] [Example 1]

[0134] Got the Figure 1The basic structure shown in FIG. 1 is provided with a pneumatic tire for a passenger car (tire nominal value = 205 / 55R16 91V) having the specifications shown in Table 1 below.

[0135] In Example 1, the ratio of the axial width of the shoulder land portion to the width WT of the tread is 17%.

[0136] The groove width w of the middle circumferential groove and the shoulder circumferential groove is 5 to 6% of the tread width WT.

[0137] The loss tangent LTb at the base is 0.10, and the loss tangent LTc at the crown is 0.27.

[0138] The ratio (DX / DY) of the axial distance DX from the shoulder circumferential groove to the circumferential narrow groove to the axial distance DY from the shoulder circumferential groove to the end of the outer layer is 50%.

[0139] The ratio of the groove width WG of the circumferential narrow groove to the tread width WT (WG / WT) is 2.0%.

[0140] The ratio of the groove depth α of the circumferential narrow groove to the tread thickness β is 90%. The groove bottom of the circumferential narrow groove is formed by the base portion. This is indicated by "Y" in the "Groove Bottom" column in Table 1.

[0141] The end of the base portion is arranged axially inward of the end of the inner layer. This is indicated by "in" in the "end of the base portion" column in Table 1.

[0142] The ratio (WB / WS) of the axial width WB of the base portion to the axial width WS of the outer layer is 100%.

[0143] [Comparative Example 1]

[0144] A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that no circumferential narrow grooves were provided in the shoulder land portion.

[0145] [Example 2-3 and Comparative Example 2-3]

[0146] Tires of Example 2-3 and Comparative Example 2-3 were obtained in the same manner as in Example 1 except that the ratio (DX / DY) was as shown in Table 1 below.

[0147] [Examples 4-6]

[0148] Tires of Examples 4 to 6 were obtained in the same manner as in Example 1 except that the ratio (WG / WT) was as shown in Table 2 below.

[0149] [Examples 7-9]

[0150] Tires of Examples 7-9 were obtained in the same manner as in Example 1, except that the ratio (α / β) was as shown in Table 2 below. In Examples 7-8, the groove bottom of the circumferential narrow groove was formed by the crown top. This is indicated by "N" in the "Groove Bottom" column in Table 2.

[0151] [Example 10]

[0152] The tire of Example 10 was produced in the same manner as in Example 1, except that the crown and base of the tread were constructed according to conventional specifications. The ends of the base were positioned axially outward of the ends of the belt. As a result, the entire belt was covered by the base. Therefore, the ends of the base were positioned axially outward of the ends of the inner layer. This is indicated by "out" in the "Ends of Base" column in Table 2. The ratio (WB / WS) was 114%. The materials of the crown and base were the same as in Example 1.

[0153] [Rolling resistance]

[0154] The rolling resistance coefficient (RRC) of the trial tire was measured using a rolling resistance tester while running on a drum at 80 km / h under the following conditions. The results are shown in the "RRC" column of Table 1-2 below, with Comparative Example 1 as 100. The larger the value, the lower the rolling resistance of the tire.

[0155] Rim: 16×6.5J

[0156] Internal pressure: 210kPa

[0157] Longitudinal load: 4.82kN

[0158] [WET performance]

[0159] The prototype tire was assembled onto a rim (size = 16 x 6.5J), filled with air, and the internal pressure of the tire was adjusted to 250 kPa. The tire was then mounted on a test vehicle (passenger car). The test vehicle was driven on a test course on a wet road surface (water film thickness = 1.4 mm), and lap times were measured. The results are shown in the "WET" column of Table 1-2 below, with Comparative Example 1 as 100. Larger values ​​indicate superior WET performance.

[0160] Durability

[0161] The test tire was assembled on a rim (size = 16 x 6.5J), filled with air and set to an internal pressure of 250 kPa. The tire was mounted on a drum-type running test machine. The tire was loaded with a longitudinal load of 7.33 kN and made to run on a drum (radius = 1.7 m) at a speed of 100 km / h. The running distance until the tire was confirmed to be damaged (BEL) was measured. The result is shown in the "BEL" column of Tables 1-2 below as an index of 100 for Comparative Example 1. The larger the value, the less likely the tire is to be damaged, and the more excellent the durability. In this evaluation, if the index is 95 or more, the generation of damage is allowed.

[0162] [Steering stability]

[0163] The test tire was assembled on a rim (size = 16 x 6.5J), filled with air and set to an internal pressure of 250 kPa. The tire was mounted on a flat-belt running test machine. The camber angle was set to 0 degrees. The tire was loaded with a longitudinal load of 4.3 kN, the slip angle was set to 1.0 degrees, and the tire was made to run on the belt at a speed of 10 km / h, and the cornering power was measured. The result is shown in the "CP" column of Tables 1-2 below as an index of 100 for Comparative Example 1. The larger the value, the greater the cornering power, and the more excellent the steering stability.

[0164] Table 1

[0165]

[0166] Table 2

[0167]

[0168] As shown in Tables 1-2, it was confirmed that the reduction in rolling resistance was achieved without reducing the WET performance in the examples, and the effect of reducing the rolling resistance was continuously exerted. The superiority of the present application was known from the evaluation results.

[0169] Industrial applicability

[0170] The technology described above, which enables the reduction in rolling resistance without reducing the WET performance, can also be applied to various tires.

Claims

1. A tire, characterized in that: The vehicle comprises a tread that contacts the road surface, and a belt layer located radially inward of the tread. The tread is provided with a plurality of circumferential grooves arranged in the axial direction, and at least three land portions are formed on the tread. The circumferential groove located most axially outward among the plurality of circumferential grooves is a shoulder circumferential groove, and the land portion located most axially outward among the at least three land portions is a shoulder land portion. The belt layer includes an inner layer and an outer layer located radially outward of the inner layer. The end of the outer layer is located axially inward of the end of the inner layer, The shoulder land portion is provided with circumferential narrow grooves extending continuously in the circumferential direction. The width of the circumferential narrow groove is narrower than the width of the shoulder circumferential groove. The circumferential narrow groove is located between the shoulder circumferential groove and the end of the outer layer in the axial direction. The ratio of the axial distance from the shoulder circumferential groove to the circumferential narrow groove to the axial distance from the shoulder circumferential groove to the end of the outer layer is 15% or more and 55% or less. The tread includes a crown portion contacting the road surface and a base portion located radially inward of the crown portion. The loss tangent of the base at 30°C is lower than the loss tangent of the crown at 30°C, The base is located radially inside the circumferential groove, The groove bottom of the circumferential narrow groove is formed by the base portion.

2. The tire according to claim 1, wherein A ratio of the groove width of the circumferential narrow groove to the width of the tread is 1.0% or more and 2.5% or less.

3. The tire according to claim 1 or 2, characterized in that A ratio of the groove depth of the circumferential narrow groove to the thickness of the tread is 20% or more and 95% or less.

4. The tire according to claim 1, wherein The end of the base portion is located axially inward of the end of the inner layer.

5. The tire according to claim 1 or 4, characterized in that A ratio of an axial width of the base portion to an axial width of the outer layer is 95% or more and 105% or less.

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