tire

Abstract

The present invention provides a tire (2) that can improve wet performance during cornering without increasing rolling resistance. The tread (4) of the tire (2) includes a crown layer (38) constituting a portion of the surface of the tire (2), an intermediate layer (40) radially located inside the crown layer (38), and a base layer (42) radially located inside the intermediate layer (40). The loss tangent at 30°C of the intermediate layer (40) is lower than the loss tangent at 30°C of the crown layer (38), and the loss tangent at 30°C of the base layer (42) is lower than the loss tangent at 30°C of the intermediate layer (40). In the axial direction, the outer end PC of the crown layer (38) is located outside the outer end PB of the base layer (42). In the radial direction, the position of the outer end PC of the crown layer (38) coincides with the position of the outer end PB of the base layer (42), or the outer end PC of the crown layer (38) is located inside the outer end PB of the base layer (42).

Description

Technical Field

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

[0002] When low-heat-generating rubber is used for the tread, a tire with low rolling resistance can be obtained. However, the grip of low-heat-generating rubber is inferior to that of heat-generating rubber that can exert high grip. Therefore, when low-heat-generating rubber is used for the tread, braking performance (hereinafter also referred to as wet performance) on a wet road surface is reduced. It is difficult to strike a good balance between rolling resistance and wet performance. Various studies have been conducted to reduce rolling resistance and improve wet performance (for example, Patent Document 1 below).

[0003]

Prior art literature

[0004] Patent Literature

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-2008 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] As vehicles increase in speed, tires are required to improve wet performance not only during straight-line driving but also during cornering. To improve wet performance, research is underway to use high-grip rubber in the tread. However, high-grip rubber tends to heat up, increasing the tire's rolling resistance. There is a need for a technology that can improve wet performance during cornering without increasing rolling resistance.

[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 improving wet performance during cornering without increasing rolling resistance.

[0009] Solutions for solving problems

[0010] A tire according to one embodiment of the present invention includes a tread for contacting a road surface. The tire surface includes a tread surface and a pair of side surfaces connected to the edges of the tread surface. In a meridian cross-section of the tire, the profile of the tread surface includes a plurality of curved contour lines formed by arcs having different radii. The tire surface profile includes: a curved portion, at an edge portion of the tread surface, formed by a curved contour line among the plurality of curved contour lines included in the tread surface profile, the curved contour line formed by an arc having the smallest radius and connected to the side surface; an inner adjacent contour line located axially inward of the curved portion and in contact with the curved portion; and an outer adjacent contour line located axially outward of the curved portion and in contact with the curved portion. The intersection of a straight line extending radially through the intersection of two tangent lines, one tangent to the curved portion at the point where the inner adjacent contour line connects to the curved portion, and the other tangent to the curved portion at the point where the outer adjacent contour line connects to the curved portion, is a tread reference end. The axial distance from the equatorial plane to the tread reference end is half the tread width. The tread includes a crown layer constituting a portion of the tire surface, an intermediate layer radially located inward of the crown layer, and a base layer radially located inward of the intermediate layer. The loss tangent of the intermediate layer at 30°C is lower than that of the crown layer, and the loss tangent of the base layer at 30°C is lower than that of the intermediate layer. In the axial direction, the outer end of the crown layer is located outward of the outer end of the base layer. In the radial direction, the position of the outer end of the crown layer coincides with the position of the outer end of the base layer, or the outer end of the crown layer is located inward of the outer end of the base layer.

[0011] Preferably, in the tire, the outer end of the intermediate layer is located outside the outer end of the base layer in the axial direction, the outer end of the intermediate layer is located coincident with the outer end of the base layer in the axial direction, or the outer end of the intermediate layer is located inside the outer end of the base layer.

[0012] In this tire, preferably, in the axial direction, the position of the outer end of the base layer coincides with the position of the tread reference end, or the outer end of the base layer is located inside the tread reference end.

[0013] Preferably, in this tire, the contact patch obtained by assembling the tire onto a regular rim, adjusting the tire's internal pressure to the regular internal pressure, and then applying a longitudinal load equal to 70% of the regular load to the tire, resulting in the tire contacting a flat road surface, is defined as a reference contact patch. Half of the contact patch width is defined as the contact patch half-width. The portion of the tire surface formed by the crown layer is defined as the crown surface. Axially, the outer end of the crown surface is located outboard of the tread reference end. In a meridian cross-section of the tire, the ratio of the sum of the length from the tread reference end to the outer end of the crown surface, as measured along the tire surface, and the tread half-width to the contact patch half-width is not less than 1.15 and not more than 1.20.

[0014] Preferably, in this tire, at the tread reference end, a ratio of the thickness of the crown layer to the thickness of the tread is not less than 15% and not more than 35%.

[0015] Preferably, in the tire, at the outer end of the crown surface, a ratio of the thickness of the crown layer to the thickness of the tread is 15% or more and 35% or less.

[0016] Preferably, the difference between the LAT wear index of the crown layer and the LAT wear index of the intermediate layer of the tire is not less than -10 and not more than 10.

[0017] Effects of the Invention

[0018] According to the present invention, a tire can be obtained that can improve wet performance during cornering without increasing rolling resistance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 Schematic diagram illustrating the ground width of a reference ground plane.

[0021] Figure 3 Yes Figure 1 An enlarged cross-sectional view of the profile of the shoulder portion of a tire.

[0022] Figure 4 Yes Figure 1 An enlarged cross-sectional view of a portion of a tire.

[0023] Figure 5 It is an enlarged cross-sectional view showing a modified example of the tread structure.

[0024] Figure 6 Yes Figure 4 An enlarged cross-sectional view of a portion of a tire.

[0025] Figure 7 This is an enlarged cross-sectional view showing a portion of the tire of Comparative Example 1.

[0026] Marking Description

[0027] 2. Tires

[0028] 4···tread

[0029] 6···Sidewall

[0030] 12···Curtain fabric

[0031] 14···Belt

[0032] 16···crown layer

[0033] 26, 26s, 26m···Circumferential groove

[0034] 28, 28s, 28m···Land Department

[0035] 34, 34a, 34b···ply

[0036] 36, 36a, 36b... layers

[0037] 38···Crown layer

[0038] 40···Middle layer

[0039] 42···basal layer

[0040] 44···Crown surface DETAILED DESCRIPTION

[0041] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0042] In the present disclosure, a state in which a tire is mounted on a regular rim, the tire internal pressure is adjusted to a regular internal pressure, and no load is applied to the tire is referred to as a regular state.

[0043] In this disclosure, unless otherwise specified, the dimensions and angles of various tire components are measured under normal conditions. Dimensions and angles of various components in a meridian cross-section of the tire, which cannot be measured when the tire is mounted on a normal rim, are measured by aligning the distance between the left and right beads in the cross-section of the tire, obtained by cutting the tire along a plane including the axis of rotation, with the distance between the beads aligned with the distance between the beads in the tire mounted on a normal rim.

[0044] A standard rim is a rim specified in the tire's specifications. Standard rims in the JATMA standard, design rims in the TRA standard, and measuring rims in the ETRTO standard are standard rims.

[0045] Normal internal pressure refers to the internal pressure specified in the tire's standards. These pressures include the "maximum pressure" 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 "INFLATION PRESSURE" in the ETRTO standard.

[0046] The normal load refers to the load specified in the tire's standards. The normal load is the "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" section in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard.

[0047] In this disclosure, cross-linked rubber refers to a molded article 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.

[0048] 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 reinforcing agents such as carbon black and 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 the tread and sidewall components to which the rubber composition is applied.

[0049] In the present disclosure, the loss tangent (also referred to as tan δ) at 30°C of a crosslinked rubber component among rubber components is measured in accordance with JIS K6394 using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions.

[0050] Initial deformation = 10%

[0051] Dynamic deformation = 2%

[0052] Frequency = 10 Hz

[0053] Deformation Mode = Stretch

[0054] In this measurement, test pieces are sampled from tires. If it is not possible to sample a test piece from a tire, a sheet of crosslinked rubber (hereinafter referred to as a rubber sheet) is obtained by pressurizing and heating the rubber composition used to form the element to be measured at 170°C for 12 minutes. The crosslinked rubber is then used to obtain a test piece.

[0055] In the present disclosure, the LAT wear index is an index for evaluating the wear resistance of rubber components among components constituting a tire. The larger the LAT wear index, the better the wear resistance of the component being evaluated.

[0056] LAT wear index is measured using a friction tester, such as LAT testers (Laboratory Abrasion and Skid Tester) such as LAT100 (VMI company system). In this measurement, in the mold for the test piece, the rubber composition for forming the element as the test object is vulcanized and molded at 170 ° C for 20 minutes to prepare the test piece. Using the test piece, the volume loss amount (volume loss amount of the evaluation object) of the test piece is measured under the conditions of a load of 50N, a speed of 20km / h, and a slip angle of 5 °. The volume loss amount (reference volume loss amount) of the rubber composition as a benchmark is also measured in the same manner. Using the volume loss amount and reference volume loss amount of the evaluation object, the LAT wear index of the evaluation object element is obtained by the following formula.

[0057] LAT wear index = (reference volume loss / evaluation object volume loss) × 100 LAT

[0058] The LAT wear index represents the volume loss of the evaluation object as an index with the reference volume loss as 100. The reference rubber composition is not particularly limited. For example, when determining the LAT wear index of a tread component, a rubber composition used to form a cap layer of a conventional tread consisting of two layers, a cap layer and a base layer, can be used as the reference rubber composition.

[0059] 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 a passenger car. Figure 1 , a portion of a cross section of the tire 2 along a plane including the rotation axis of the tire 2 (hereinafter also referred to as a meridian cross section) is shown. Figure 1 , the left-right direction is the axial direction of the tire 2 , and the up-down direction is the radial direction of the tire 2 . Figure 1 The direction perpendicular to the paper surface is the circumferential direction of the tire 2 .

[0060] exist Figure 1 In FIG, the dot-dash line EL is the equatorial plane of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane except for decorations such as tread patterns, designs, and texts engraved on its surface.

[0061] exist Figure 1 In the figure, tire 2 is assembled on rim R. Rim R is a regular rim. The interior of tire 2 is filled with air to regulate the internal pressure of tire 2. The tire 2 assembled on rim R is also called a tire-rim assembly. The tire-rim assembly includes rim R and tire 2 assembled on rim R.

[0062] exist Figure 1 In FIG, the position indicated by the symbol PW is the axial outer end of the tire 2. When a pattern, text, or other device is located on the surface, the outer end PW is determined based on an imaginary surface obtained by assuming that there is no decoration.

[0063] exist Figure 1 In the diagram, the length indicated by the symbol WA represents the maximum width of the tire 2, i.e., the cross-sectional width (see JATMA, etc.). The cross-sectional width WA of the tire 2 is the axial distance from the outer end PW on one side to the outer end PW on the other side. The outer end PW is the position indicating the maximum width of the tire 2 (hereinafter referred to as the maximum width position). The cross-sectional width WA is measured for the tire 2 in a normal condition.

[0064] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of beadlets 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a cap ply 16 , a pair of breaker layers 18 , a pair of chafers 20 , and an inner liner 22 .

[0065] The tread 4 contacts the road surface on its surface. The tread 4 is engraved with grooves 24. This constitutes a tread pattern.

[0066] In the tire 2, at least three circumferential grooves 26 extending continuously in the circumferential direction are engraved on the tread 4. Thus, at least four land portions 28 arranged in parallel in the axial direction are formed on the tread 4. Figure 1 In the tire 2 shown, three circumferential grooves 26 are engraved on the tread 4 to form four land portions 28. The circumferential grooves 26 form a part of the grooves 24 constituting the tread pattern.

[0067] exist Figure 1 In FIG, the position indicated by the symbol PE is the equator of the tire 2. The equator PE is the intersection line between the surface of the tread 4 and the equatorial plane. Figure 1 As shown, in the case where the grooves 24 are present on the equatorial plane, the equatorial PE is determined based on an imaginary surface obtained by assuming that the tread 4 does not have the grooves 24 .

[0068] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the edge of the tread 4 along the cord 12 toward the bead 8. The sidewall 6 is formed of a cross-linked rubber with consideration given to cut resistance.

[0069] Each bead 8 is located radially inward of the sidewall 6. The bead 8 contacts the rim R. The bead 8 is made of a cross-linked rubber that takes wear resistance into consideration.

[0070] Each bead 10 is located axially inside the nozzle 8. The bead 10 includes a bead core 30 and an apex bead 32. Although not shown, the bead core 30 includes a steel wire.

[0071] The apex bead 32 is located radially outside the bead core 30. The apex bead 32 tapers outward. The apex bead 32 is formed of a cross-linked rubber having high rigidity.

[0072] The cord 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of beads 8. The cord 12 spans between one bead 10 and the other bead 10. The cord 12 has a radial structure.

[0073] The carcass 12 includes at least one carcass layer 34. From the viewpoint of weight reduction, the carcass 12 of the tire 2 is composed of one carcass layer 34.

[0074] The carcass ply 34 includes a main layer 34a and a pair of folded portions 34b. The main layer 34a spans between one bead core 30 and the other bead core 30. Each folded portion 34b is connected to the main layer 34a and folded back from the axial inside to the outside at each bead core 30. In this tire 2, the edge of the folded portion 34b is located radially outside the maximum width position PW.

[0075] Although not shown, the carcass ply 34 includes a plurality of parallel cords. These cords are covered with a rubber tip. Each cord intersects the equatorial plane. The cords are made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0076] The belt layer 14 is located radially inside the tread 4. The belt layer 14 is accumulated from the cut side to the cord 12 in the radial direction. Figure 1 , 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 this 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.

[0077] The belt layer 14 is composed of at least two layers 36 stacked in the radial direction. The belt layer 14 of the tire 2 is formed by two layers 36 stacked in the radial direction. Of the two layers 36, the layer 36 located on the inner side is the inner layer 36a, and the layer 36 located on the outer side is the outer layer 36b. Figure 1 As shown, the inner layer 36a is wider than the outer layer 36b. The length from the edge of the outer layer 36b to the edge of the inner layer 36a is 3 mm to 10 mm.

[0078] Although not shown, the inner layer 36a and the outer layer 36b each include multiple belt cords arranged in parallel. These belt cords are covered with top rubber. Each belt cord is inclined relative to the equatorial plane. The belt cords are made of steel.

[0079] The cap layer 16 is located between the tread 4 and the belt layer 14 in the radial direction. The cap layer 16 is stacked on the belt layer 14 on the inner side of the tread 4.

[0080] Although not shown, the cap ply 16 includes helically wound cap ply cords. The cap ply cords extend substantially in the circumferential direction. Specifically, the cap ply cords form an angle of 5° or less with the circumferential direction. The cap ply 16 has a seamless structure. In this tire 2, cords formed from organic fibers are used as the cap ply cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0081] The cap ply 16 of the tire 2 is formed of full cap plies with opposite ends sandwiching the equatorial PE. The cap ply 16 is wider than the belt 14. The length from the edge of the belt 14 to the edge of the cap ply 16 is 3 mm to 10 mm. The cap ply 16 covers the entire belt 14. The cap plies 16 are spaced apart in the axial direction and may include a pair of sidebands that cover the edges of the full cap ply and the edges of the belt 14. The cap ply 16 may consist solely of a pair of sidebands.

[0082] The breaker layers 18 are spaced apart in the axial direction. The breaker layers 18 are located between the edges of the belt layer 14 and the band ply 16 and the main layer 34a of the carcass 12. The breaker layers 18 are formed of a cross-linked rubber having low rigidity.

[0083] Each chafer 20 is located radially inward of the rim 10. The chafer 20 is in contact with the rim R. The chafer 20 of the tire 2 is formed of cloth and rubber impregnated with the cloth.

[0084] The inner liner 22 is located inside the carcass 12. The inner liner 22 forms the inner surface of the tire 2. The inner liner 22 is made of a cross-linked rubber having a low gas permeability coefficient. The inner liner 22 maintains the internal pressure of the tire 2.

[0085] exist Figure 1, the position indicated by symbol PH is located on the surface of the tread 4. The position PH corresponds to the axially outer end of the contact surface between the tire 2 and the road surface.

[0086] The contact patch used to determine position PH is obtained using, for example, a contact patch shape measuring device (not shown). This contact patch is obtained by applying a longitudinal load of 70% of the normal load to the tire 2, with the camber angle of the tire 2 in its normal state set to 0°, and causing the tire 2 to contact a flat road surface. The contact patch thus obtained in the tire 2 serves as a reference contact patch, and the position on the surface of the tread 4 corresponding to the axially outer end of this reference contact patch is the aforementioned position PH. In the tire 2, this position PH serves as the reference contact end.

[0087] Figure 2 Schematic diagram showing the reference ground plane. Figure 2 , the up-down direction corresponds to the circumferential direction of the tire 2 , and the left-right direction corresponds to the axial direction of the tire 2 . Figure 2 The direction perpendicular to the paper plane corresponds to the radial direction of the tire 2 .

[0088] exist Figure 2 In the figure, the length denoted by the symbol CW is the ground plane width of the reference ground plane. Ground plane width CW is the axial distance from one reference ground terminal PH to the other reference ground terminal PH. Ground plane width CW represents the maximum width of the reference ground plane. In this disclosure, half of ground plane width CW is also referred to as ground plane half width HCW.

[0089] Figure 3 express Figure 1 A portion of a tire 2 is shown. Figure 3 , the left-right direction is the axial direction of the tire 2 , and the up-down direction is the radial direction of the tire 2 . Figure 3 The direction perpendicular to the paper surface is the circumferential direction of the tire 2 .

[0090] Figure 3 The figure shows the outline of the shoulder portion of the tire 2 in a meridian cross section. Figure 3 The profile shown is obtained by measuring the surface shape of the tire 2 in a normal state using a displacement sensor.

[0091] In a meridian cross-section, the profile of the tire 2 surface (hereinafter referred to as tire surface TS) is formed by connecting a plurality of 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 straight contour lines, and contour lines formed by circular arcs are referred to as curved contour lines.

[0092] The tire surface TS includes a tread surface T and a pair of side surfaces S connected to the edges of the tread surface T. In a meridian cross-section, the profile of the tread surface T includes multiple curved contour lines having different radii. In this tire 2, the curved contour line with the smallest radius among the multiple curved contour lines included in the profile of the tread surface T is located at the edge of the tread surface T and connected to the side surfaces S. In a meridian cross-section, the profile of the tire surface TS includes a curved portion at the edge of the tread surface T, formed by an arc with the smallest radius among the multiple curved contour lines included in the profile of the tread surface T, and connected to the side surfaces S. Figure 3 This curved portion is represented by symbol RS.

[0093] In the profile of the tire surface TS, the curved portion RS is in contact with a contour line adjacent to the curved portion RS along its axial inner side (hereinafter referred to as the inner adjacent contour line NT) at a connection point CT. The curved portion RS is in contact with a contour line adjacent to the curved portion RS along its axial outer side (hereinafter referred to as the outer adjacent contour line NS) at a connection point CS, forming the profile of the side surface S. The profile of the tire surface TS includes the inner adjacent contour line NT located axially inward of the curved portion RS and in contact with the curved portion RS, and the outer adjacent contour line NS located axially outward of the curved portion RS and in contact with the curved portion RS.

[0094] exist Figure 3 In the figure, the solid line LT is a tangent to the curved portion RS at the connection point CT between the inner adjacent contour line NT and the curved portion RS. The solid line LS is a tangent to the curved portion RS at the connection point CS between the outer adjacent contour line NT and the curved portion RS. The position indicated by the symbol PT is the intersection of the tangent lines LT and LS. In this tire 2, this intersection point PT is the imaginary tread end. The position indicated by the symbol Pe is the intersection of a straight line passing through the imaginary tread segment PT and diffracted in the radial direction with the tire surface TS. This intersection point Pe is the tread reference end.

[0095] exist Figure 1 In the figure, the length indicated by the double arrow WT is the width of the tread 4. The width of the tread 4 is the axial distance from one tread reference end Pe to the other tread reference end Pe. In this tire 2, the ratio of the width WT of the tread 4 to the cross-sectional width WA (WT / WA) is 70% or more and 90% or less.

[0096] In the tread 4, the portion from one tread reference end Pe to the other tread reference end Pe is the area expected to come into contact with the road surface under normal driving conditions of the tire 2 (hereinafter referred to as the normal ground contact area). From the perspective of effectively reinforcing the portion of the tread 4 (hereinafter referred to as the tread portion), the belt layer 14 and the cap layer 16 are arranged in this normal ground contact area. Figure 1As shown, the position of the edge of the cap ply 16 in the axial direction is substantially aligned with the position of the tread reference end Pe. In this tire 2, the cap ply 16 has an axial width that is equal to the width WT of the tread 4. Specifically, the difference between the width WT of the tread 4 and the axial width of the cap ply 16 is not less than -10 mm and not more than 10 mm.

[0097] exist Figure 1 In FIG. 1 , the length indicated by the double arrow WH is the axial length of the reference ground plane. The axial width WH is the axial distance from one reference ground terminal PH to another reference ground terminal PH.

[0098] In the tire 2, the tread reference end Pe is located axially outward of the reference ground contact end PH. In other words, the axial width WH of the reference ground contact surface is narrower than the width WT of the tread 4. Specifically, the ratio of the axial width WH to the width WT of the tread 4 (WH / WT) is 70% to 90%.

[0099] As described above, the tread 4 of the tire 2 has three circumferential grooves 26. In the tire 2, the arrangement, groove depth, and groove width of the three circumferential grooves 26 are not particularly limited. The tread 4 can be applied to the circumferential grooves of a typical tire using the same arrangement, groove depth, and groove width as those of the conventional tires.

[0100] In this tire 2, the circumferential groove 26 located on the outer side in the axial direction of the three circumferential grooves 26 is the shoulder circumferential groove 26s, and the circumferential groove 26 located on the inner side of the shoulder circumferential groove 26s is the center circumferential groove 26m.

[0101] As described above, the tread 4 of the tire 2 is formed with four land portions 28 . Of the four land portions 28 , the land portion 28 located on the equatorial plane side is the center land portion 28 m , and the land portion 28 located outside the center land portion 28 m is the shoulder land portion 28 s .

[0102] The shoulder land portion 28s includes a reference ground contact edge PH. Between the left and right center land portions 28m is a central circumferential groove 26m. In this tire 2, the central circumferential groove 26m is located on the equatorial plane. This central circumferential groove 26m is also referred to as a center circumferential groove.

[0103] Figure 4 express Figure 1 A portion of a tire 2 is shown. Figure 4 Indicates the tread portion of the tire 2. Figure 4 , the left-right direction is the axial direction of the tire 2 , and the up-down direction is the radial direction of the tire 2 . Figure 4 The direction perpendicular to the paper is the circumferential direction of the tire 2. Figure 4In FIG, the length indicated by symbol HWT is the axial distance from the equatorial plane to the tread reference end Pe. This axial distance HWT is half of the width WT of the tread 4 described above, and is also called the tread half width.

[0104] The tread 4 of the tire 2 includes a crown layer 38, an intermediate layer 40, and a base layer 42. The crown layer 38 constitutes a portion of the tire surface TS. The intermediate layer 40 is located radially inward of the crown layer 38. The base layer 42 is located radially inward of the intermediate layer 40. Figure 4 As shown, the crown layer 38 is stacked on the intermediate layer 40, and the intermediate layer 40 is stacked on the base layer 42. The crown layer 38, the intermediate layer 40, and the base layer 42 are configured to have substantially the same thickness except near the tread reference end Pe described later.

[0105] exist Figure 4 In the figure, the position indicated by the symbol PC is the outer end of the crown layer 38. The length indicated by the symbol WC is the axial width of the crown layer 38. The axial width WC is the axial distance from one outer end PC to the other outer end PC. The position indicated by the symbol PM is the outer end of the middle layer 40. The length indicated by the symbol WM is the axial width of the middle layer 40. The axial width WM is the axial distance from one outer end PM to the other outer end PM. The position indicated by the symbol PB is the outer end of the base layer 42. The length indicated by the symbol WB is the axial width of the base layer 42. The axial width WB is the axial distance from one outer end PB to the other outer end PB.

[0106] As described above, the crown layer 38 constitutes a portion of the tire surface TS. Within the tire surface TS, the portion constituted by the crown layer 38 is the crown surface 44. The position indicated by the symbol PF is the outer end of the crown surface 44. In the tire 2, the outer end PF of the crown surface 44 is axially located outward from the tread reference end Pe. The outer end PC of the crown layer 38 is radially located inward from the outer end PF of the crown surface 44. The outer end PC of the crown layer 38 does not lie on the tire surface TS. If the outer end PC of the crown layer 38 lies on the tire surface TS, the outer end PC of the crown layer 38 also constitutes the outer end PF of the crown surface 44.

[0107] exist Figure 4 , the position indicated by symbol PS is the outer end of the tread 4 on the tire surface TS. In this tire 2, the outer end PF of the crown surface 44 coincides with the outer end PS of the tread 4. In this tire 2, the intermediate layer 40 located on the inner side of the crown layer 38 is not exposed to the tire surface TS.

[0108] In this tire 2, the outer end PC of the crown layer 38 coincides radially with the outer end PM of the intermediate layer 40. The outer end PC of the crown layer 38 coincides axially with the outer end PM of the intermediate layer 40. In this tire 2, the position of the outer end PC of the crown layer 38 can be appropriately adjusted between the outer end PF of the crown surface 44 and the outer end PM of the intermediate layer 40, taking into account the impact on the performance of the tire 2.

[0109] In this tire 2, the outer end PM of the intermediate layer 40 is located axially outside the edge of the belt layer 14. The edge of the cap ply 16 is located between the outer end PM of the intermediate layer 40 and the edge of the belt layer 14. In this tire 2, the intermediate layer 40 covers the edges of the belt layer 14 and the cap ply 16. In particular, from the perspective of preventing damage to the edge of the belt layer 14, the length from the edge of the belt layer 14 to the outer end PM of the intermediate layer 40 is preferably 10 mm or more and preferably 15 mm or less.

[0110] In this tire 2, a base layer 42 is laminated on the cap layer 16. The base layer 42 is reinforced by the cap layer 16 and the belt layer 14 located inside the cap layer 16. From the viewpoint of effective reinforcement, in this tire 2, the axial width WB of the base layer 42 is preferably the same as or narrower than the axial width of the cap layer.

[0111] In this tire 2, the crown layer 38, the intermediate layer 40, and the base layer 42 are each formed from a cross-linked rubber having different heat generation properties. In this tire 2, the crown layer 38 is most susceptible to heat generation, while the base layer 42 is least susceptible to heat generation. The intermediate layer 40 has a heat generation property intermediate between the heat generation properties of the crown layer 38 and the base layer 42. In this tire 2, the loss tangent (LTm) at 30°C of the intermediate layer 40 is lower than the loss tangent (LTc) at 30°C of the crown layer 38. The loss tangent (LTb) at 30°C of the base layer 42 is lower than the loss tangent (LTm) at 30°C of the intermediate layer 40.

[0112] The loss tangent LTb of the base layer 42 at 30°C is preferably 0.11 or less. This is because it effectively contributes to reducing the rolling resistance of the base layer 42. From this perspective, the loss tangent LTb is more preferably 0.10 or less, and even more preferably 0.09 or less. A lower loss tangent LTb of the base layer 42 is preferred, so there is no preferred lower limit.

[0113] The loss tangent LTm of the intermediate layer 40 at 30°C is preferably 0.15 or less. This is because it effectively contributes to reducing the rolling resistance of the intermediate layer 40. 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 40 at 30°C is preferably 0.11 or greater. This is because it ensures the required rigidity of the intermediate layer 40 and effectively contributes to improving wet performance. From this perspective, the loss tangent LTm is preferably 0.12 or greater.

[0114] The loss tangent LTc of the crown layer 38 at 30°C is preferably 0.15 or more. This is because the crown layer 38 can contribute to the improvement of wet performance. From this point of view, the loss tangent LTc is more preferably 0.16 or more, and further preferably 0.17 or more. The crown layer 38 is in contact with the road surface. From the viewpoint of improving wet performance, the higher the loss tangent LTc, the more preferable. However, an excessively high loss tangent LTc causes heat generation. There is a concern that the heated crown layer 38 will increase the temperature of the intermediate layer 40 to a level higher than expected. From the viewpoint of stably maintaining the temperature state of the entire tread 4 and being able to maintain low rolling resistance, the loss tangent LTc of the crown layer 38 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and further preferably 0.27 or less.

[0115] In this tire 2, the outer end PC of the crown layer 38 is located axially outward from the outer end PB of the base layer 42. Furthermore, in the radial direction, the position of the outer end PC of the crown layer 38 coincides with the position of the outer end PB of the base layer 42, or the outer end PC of the crown layer 38 is located inward from the outer end PB of the base layer 42. In this tire 2, the crown layer 38 is configured so that the crown layer 38 surrounds the base layer 42 from the outside in the radial direction.

[0116] Of the tire surface TS, the portion intended to come into contact with the road surface is formed by the tread 4. In this tire 2, this portion is formed by the crown layer 38. In other words, the edge of the portion intended to come into contact with the road surface is the outer end PF of the crown surface 44. In this tire 2, the crown layer 38 also comes into contact with the road surface during cornering. This tire 2 improves wet performance during cornering.

[0117] In this tire 2, the crown layer 38 comes into contact with the road surface not only during straight-line driving but also during cornering. Because the crown layer 38 uses a rubber with high grip, this tire 2 can construct the intermediate layer 40 located inside the crown layer 38 with a rubber that slightly sacrifices grip and prioritizes low heat buildup, rather than a rubber that easily heats up and prioritizes grip. In this tire 2, while the outer portion of the tread 4 is constructed with the crown layer 38, which easily heats up, the intermediate layer 40 located inside the crown layer 38 contributes to reducing rolling resistance. This tire 2 improves wet performance during cornering without increasing rolling resistance.

[0118] In this tire 2, the outer end PM of the intermediate layer 40 is located axially outward from the outer end PB of the base layer 42. In the radial direction, the outer end PM of the intermediate layer 40 is located radially inward from the outer end PB of the base layer 42. Although not shown, the position of the outer end PM of the intermediate layer 40 may coincide with the position of the outer end PB of the base layer 42 in the radial direction.

[0119] In this tire 2, the intermediate layer 40 is arranged so that it radially surrounds the base layer 42 from the outside. As described above, the crown layer 38 is arranged so that it radially surrounds the intermediate layer 40 from the outside. In other words, the crown layer 38 covers the intermediate layer 40 from the outside, and the intermediate layer 40 covers the base layer 42 from the outside. In this tire 2, the intermediate layer 40 is effectively positioned between the crown layer 38 and the base layer 42 at the edge of the tread 4, which is actively moving during running. The intermediate layer 40, which is less susceptible to heat generation than the crown layer 38, effectively contributes to reducing rolling resistance. The intermediate layer 40 takes grip into consideration, ensuring the required wet performance during cornering even if the crown layer 38 wears. From the perspective of reducing rolling resistance and ensuring wet performance, in this tire 2, it is preferred that in the axial direction, the outer end PM of the middle layer 40 is located outside the outer end PB of the base layer 42, and in the radial direction, the position of the outer end PM of the middle layer 40 is consistent with the position of the outer end PB of the base layer 42, or the outer end PM of the middle layer 40 is located inside the outer end PB of the base layer 42.

[0120] During cornering (hereinafter also referred to as "severe cornering"), which generates large inertial forces, the vehicle's rolling motion causes the portion of the tread 4 further outward from the tread reference end Pe to come into contact with the road surface, causing wear on this outer portion. Consequently, during severe cornering, there is a concern that the base layer 42 may be exposed due to wear on this outer portion. Exposure of the base layer 42 creates a risk of tread 4 peeling off, originating from the base layer 42. Therefore, tires are required to demonstrate not only wet performance during cornering but also durability during severe cornering.

[0121] like Figure 4As shown, in the tire 2, the position of the outer end PB of the base layer 42 in the axial direction coincides with the position of the tread reference end Pe. Figure 5 As shown, the outer end PB of the base layer 42 may be located inward of the tread reference end Pe.

[0122] In this tire 2, the base layer 42 is arranged at a position separated from the tire surface TS in the edge portion of the tread 4. This prevents the base layer 42 from being exposed even if the portion outside the tread reference end Pe wears during sharp cornering. This tire 2 improves durability during sharp cornering. From this perspective, in this tire 2, it is preferred that the outer end PB of the base layer 42 be aligned with the tread reference end Pe in the axial direction, or be located inward of the tread reference end Pe.

[0123] As described above, in this tire 2, the middle layer 40 is located between the crown layer 38 and the base layer 42. The middle layer 40 heats up more easily than the base layer 42, but heats up less easily than the crown layer 38. This tire 2 can reduce rolling resistance and improve durability during sharp cornering.

[0124] exist Figure 5 In the diagram, the length denoted by symbol α is the axial distance from the tread reference end Pe to the outer end PB of the base layer 42. This axial distance α is represented by a positive number when the outer end PB of the base layer 42 is located outside the tread reference end Pe, and is represented by a negative number when the outer end PB of the base layer 42 is located inside the tread reference end Pe.

[0125] In this tire 2, when the outer end PB of the base layer 42 is located inward of the tread reference end Pe, from the perspective of reducing rolling resistance, the ratio of the axial distance α to the tread half width HWT (α / HWT) is preferably -10.0% or greater, and more preferably -6.0% or greater. From the perspective of improving durability during severe cornering, this ratio (α / HWT) is preferably 3.0% or less, and more preferably 0.0% or less.

[0126] exist Figure 4 In FIG. 4 , the length indicated by symbol β is the length from the tread reference end Pe to the outer end PF of the tread crown surface 44. The length β is measured along the tire surface TS in a meridian cross section of the tire 2.

[0127] In the tire 2, the ratio ((β+HWT) / HCW) of the sum of the length β from the tread reference end Pe to the outer end PF of the crown surface 44 and the tread half width HWT (β+HWT) to the ground contact half width HCW is preferably 1.15 or more and 1.20 or less.

[0128] By setting ((β + HWT) / HCW) to 1.15 or greater, the portion that contacts the road surface during cornering is formed by the crown layer 38. This tire 2 improves wet performance during cornering. From this perspective, the ratio ((β + HWT) / HCW) is more preferably 1.16 or greater.

[0129] By setting ((β + HWT) / HCW) to 1.20 or less, the volume of the crown layer 38 included in the edge portion of the tread 4 can be appropriately maintained. In this tire 2, the influence of the crown layer 38 on rolling resistance is suppressed. From this viewpoint, the ratio ((β + HWT) / HCW) is more preferably 1.19 or less.

[0130] Figure 6 express Figure 4 A portion of a tire 2 is shown. Figure 6 Indicates the shoulder portion of the tire 2. Figure 6 , the left-right direction is the axial direction of the tire 2 , and the up-down direction is the radial direction of the tire 2 . Figure 6 The direction perpendicular to the paper surface is the circumferential direction of the tire 2 .

[0131] exist Figure 6 In the figure, the solid line Le is the normal line to the tire surface TS passing through the tread reference end Pe. The length indicated by the double-headed arrow X is the thickness of the tread 4 measured along the normal line Le. This thickness X is the thickness of the tread 4 at the tread reference end Pe. The length indicated by the double-headed arrow x is the thickness of the crown layer 38 measured along the normal line Le. This thickness x is the thickness of the crown layer 38 at the tread reference end Pe.

[0132] In the tire 2 , at the tread reference end Pe, the ratio (x / X) of the thickness x of the crown layer 38 to the thickness X of the tread is preferably 15% or more and 35% or less.

[0133] By setting the ratio (x / X) to 15% or greater, the necessary thickness of the crown layer 38 at the tread reference end Pe can be ensured. In this tire 2, the crown layer 38 effectively contributes to improving wet performance during cornering. From this perspective, the ratio (x / X) is preferably 20% or greater.

[0134] By setting the ratio (x / X) to 35% or less, the crown layer 38 at the tread reference end Pe can maintain an appropriate thickness. In this tire 2, the effect of the crown layer 38 on rolling resistance is effectively suppressed. From this perspective, the ratio (x / X) is preferably 30% or less.

[0135] exist Figure 6In FIG, the solid line LF is a normal line to the tire surface TS passing through the outer end PF of the crown surface 44. The length indicated by the double-headed arrow Y is the thickness of the tread 4 measured along the normal line LF. This thickness Y is the thickness of the tread 4 at the outer end PF of the crown surface 44. The length indicated by the double-headed arrow y is the thickness of the crown layer 38 measured along the normal line LF. This thickness y is the thickness of the crown layer 38 at the outer end PF of the crown surface 44.

[0136] In the tire 2 , at the outer end PF of the crown surface 44 , the ratio (y / Y) of the thickness y of the crown layer 38 to the thickness Y of the tread is preferably 15% or more and 35% or less.

[0137] By setting the ratio (y / Y) to 15% or greater, the crown layer 38 at the outer end PF of the crown surface 44 can maintain the required thickness. In this tire 2, the crown layer 38 effectively contributes to improving wet performance during cornering. From this perspective, the ratio (y / Y) is preferably 20% or greater.

[0138] By setting the ratio (y / Y) to 35% or less, the crown layer 38 at the outer end PF of the crown surface 44 can maintain an appropriate thickness. In this tire 2, the effect of the crown layer 38 on rolling resistance is effectively suppressed. From this perspective, the ratio (y / Y) is preferably 30% or less.

[0139] In this tire 2, the portion of the tread 4 formed by the crown layer 38 and the intermediate layer 40 corresponds to the crown layer of the tread of a conventional tire formed by the crown layer and the base layer. To ensure that the tread 4 can effectively contribute to improved wet performance and reduced rolling resistance, the ratio (LTc / LTm) of the loss tangent LTc of the crown layer 38 at 30°C to the loss tangent LTm of the intermediate layer 40 at 30°C is preferably 110% or more and 250% or less. This ratio (LTc / LTm) is more preferably 130% or more, and even more preferably 150% or more. This ratio (LTc / LTm) is more preferably 240% or less, and even more preferably 230% or less.

[0140] In this tire 2, if the wear resistance of the crown layer 38 conflicts with that of the intermediate layer 40, there is a concern that the wear rates of the two layers may differ during sudden cornering. In this case, a step may form near the boundary between the crown layer 38 and the intermediate layer 40, creating a risk of damage originating from this step. To improve durability during sudden cornering, the LAT wear index of the crown layer and the intermediate layer are preferably comparable. Specifically, the difference between the LAT wear index of the crown layer and the intermediate layer is preferably between -10 and 10.

[0141] As described above, according to the present invention, a tire can be obtained that can improve wet performance during rolling without increasing rolling resistance.

[0142] Example

[0143] 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 these Examples.

[0144] [Example 1]

[0145] A pneumatic tire for a passenger car (tire size = 205 / 55R16) was obtained, which had Figure 1 The basic structure shown has the specifications shown in the following Table 1. The tread half width HWT is 89 mm, and the ground contact half width HCW is 80 mm.

[0146] It uses a crown layer, an intermediate layer and a base layer, Figure 4 The tread of the structure shown has a loss tangent LTc of 0.27 at 30°C for the cap layer, a loss tangent LTm of 0.12 at 30°C for the middle layer, and a loss tangent LTb of 0.10 at 30°C for the base layer.

[0147] In this Example 1, the ratio of the axial distance α from the tread reference end Pe to the outer end PB of the base layer to the tread half-width HWT (α / HWT) is 0.0%. The ratio of the sum of the length β from the tread reference end Pe to the outer end PC of the crown surface and the tread half-width HWT (β+HWT) to the ground contact half-width HCW ((β+HWT) / HCW) is 1.18. At the tread reference end Pe, the ratio of the thickness x of the crown layer to the thickness X of the tread (x / X) is 20%. At the outer end PF of the crown surface, the ratio of the thickness y of the crown layer to the thickness Y of the tread (y / Y) is 20%. The difference between the LAT wear index of the crown layer and the LAT wear index of the intermediate layer (LATc-LATm) is 0.

[0148] [Comparative Example 1]

[0149] The tread composition is set as follows Figure 7 A tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the ratio (α / HWT), the ratio ((β+HWT) / HCW), the ratio (x / X), and the ratio (y / Y) were as shown in Table 1 below. The tread structure of Comparative Example 1 was the structure of the conventional art.

[0150] [Examples 2-3]

[0151] The tire of Example 2-3 was obtained in the same manner as in Example 1 except that the ratio (α / HWT) was set as shown in Table 1 below.

[0152] [Example 4]

[0153] A tire of Example 4 was obtained in the same manner as in Example 1 except that the ratio ((β+HWT) / HCW) was set as shown in Table 2 below.

[0154] [Examples 5-6]

[0155] Tires of Examples 5-6 were obtained in the same manner as in Example 1 except that the ratio (x / X) and the ratio (y / Y) were set as shown in Table 2 below.

[0156] [Example 7]

[0157] A tire of Example 7 was obtained in the same manner as in Example 1 except that the crown layer was formed with a rubber composition having improved grip and the difference (LATc - LATm) was set as shown in Table 2. The loss tangent LTc at 30°C of the crown layer of Example 7 was 0.30.

[0158] Rolling resistance coefficient (RRC)

[0159] Using a rolling resistance tester, the prototype tires were run on a roller at 80 km / h under the following conditions, and their rolling resistance coefficients (RRC) were measured. The results are shown as indices in Tables 1 and 2. The larger the value, the lower the rolling resistance of the tire.

[0160] Rim: 16×6.5J

[0161] Internal pressure: 250kPa

[0162] Longitudinal load: 4.82kN

[0163] [Durability during sharp turns (DRY)]

[0164] The trial tire is assembled on a rim (size = 16×7J), filled with air, and the internal pressure of the tire is adjusted to 250kPa. The tire is installed on a test vehicle (passenger car). The test vehicle is rotated in an understeering state on a circular test route on a dry road. The driving speed is set to 100km / h. After driving 30 laps, the wear of the reinforcement part of the tire is confirmed and evaluated based on the number and length of cracks. The results are shown in Table 1-2 below. The larger the numerical value, the better the durability during severe steering. In this evaluation, setting an index of 100 or above is the qualified standard.

[0165] [Wet performance during cornering (WET)]

[0166] The prototype tire was assembled on a rim (size = 16×7J), filled with air, and the internal pressure of the tire was adjusted to 250kPa. The tire was mounted on a test vehicle (passenger car). The test vehicle was driven on a test course on a wet road surface (water film thickness = 1.4mm) and the lap time was measured. The results are shown in Table 1-2 below as an index. The larger the value, the better the wet performance during steering. In this evaluation, an index of 100 or above is set as the passing standard.

[0167]

Table 1

[0168]

[0169]

Table 2

[0170]

[0171] As shown in Table 1-2, it was confirmed that the Examples can provide a tire that can improve wet performance during cornering without increasing rolling resistance. The superiority of the present invention is evident from these evaluation results.

[0172] Industrial Applicability

[0173] The above-described technology capable of improving wet performance during cornering without increasing rolling resistance can also be applied to various tires.

Claims

1. A tire having a tread that contacts a road surface, characterized in that: The tire surface includes a tread surface and a pair of side surfaces connected to edges of the tread surface. In the meridian cross-section of the tire, the profile of the tread surface includes a plurality of curved contour lines formed by arcs having different radii, The profile of the tire surface includes: a curved portion, which is formed of a curved contour line at an edge portion of the tread surface, among a plurality of curved contour lines included in the profile of the tread surface, the curved contour line being formed of a circular arc having a minimum radius and connected to the side surface; an inner adjacent contour line, which is located axially inside the curved portion and is in contact with the curved portion; and an outer adjacent contour line, which is located axially outside the curved portion and is in contact with the curved portion. The intersection of a straight line extending radially through the intersection of two tangent lines and the surface of the tire is a tread reference end, wherein the two tangent lines are: a tangent line of the curved portion at the connection point of the inner adjacent contour line and the curved portion, and a tangent line of the curved portion at the connection point of the outer adjacent contour line and the curved portion. The axial distance from the equatorial plane to the reference end of the tread is half the tread width. The tread includes a crown layer constituting a portion of the tire surface, an intermediate layer located radially inward of the crown layer, and a base layer located radially inward of the intermediate layer. The loss tangent of the intermediate layer at 30°C is lower than that of the crown layer at 30°C, and the loss tangent of the base layer at 30°C is lower than that of the intermediate layer at 30°C. In the axial direction, the outer end of the crown layer is located outside the outer end of the base layer. In the radial direction, the position of the outer end of the crown layer is consistent with the position of the outer end of the base layer, or the outer end of the crown layer is located inside the outer end of the base layer. The tire is assembled onto a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and 70% of the regular load is applied as a longitudinal load to the tire, so that the tire contacts a flat road surface to obtain a ground contact surface as a reference ground contact surface. Half of the grounding width of the reference ground plane is the grounding half width, In the surface of the tire, the portion consisting of the crown layer is the crown surface. In the axial direction, the outer end of the crown surface is located outside the tread reference end. In the meridian cross section of the tire, a ratio of the sum of the length from the tread reference end to the outer end of the crown surface measured along the surface of the tire and the tread half width relative to the ground contact half width is 1.15 to 1.

20.

2. The tire according to claim 1, wherein In the axial direction, the outer end of the intermediate layer is located outside the outer end of the base layer. In the radial direction, the position of the outer end of the intermediate layer coincides with the position of the outer end of the base layer, or the outer end of the intermediate layer is located inside the outer end of the base layer.

3. The tire according to claim 1 or 2, characterized in that In the axial direction, the position of the outer end of the base layer coincides with the position of the tread reference end, or the outer end of the base layer is located on the inner side of the tread reference end.

4. The tire according to claim 1 or 2, characterized in that At the tread reference end, a ratio of the thickness of the crown layer to the thickness of the tread is not less than 15% and not more than 35%.

5. The tire according to claim 4, characterized in that At an outer end of the crown surface, a ratio of a thickness of the crown layer to a thickness of the tread is not less than 15% and not more than 35%.

6. The tire according to claim 1 or 2, characterized in that The difference between the LAT wear index of the crown layer and the LAT wear index of the intermediate layer is not less than -10 and not more than 10, The LAT wear index is an index for evaluating the wear resistance of rubber components among components constituting a tire.

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