tire

Abstract

To provide a tire that can make both wet performance and wear resistance thereof comparable.SOLUTION: A tire 1 comprises a plurality of circumferential grooves 21 and 22 and a plurality of land parts 31-33 partitioned by the plurality of circumferential grooves 21 and 22. A tire outer radius OD[mm] is in a range of 200≤OD≤660, and a total width SW[mm] of the tire is in a range of 100≤SW≤400. At least one of the plurality of circumferential grooves 21 and 22 has a groove shape formed by alternately connecting wide parts 211, 221 to narrow parts 212, 222. Groove widths W1[mm] of the wide parts 211 and 221 are in a range of 0.025≤W1 / SW≤0.070 with respect to the total width SW[mm] of the tire, and groove widths W2[mm] of the narrow parts 212 and 222 are in a range of 0.001≤W2 / SW≤0.024 with respect to the total width SW[mm] of the tire.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire that can achieve both wet performance and wear resistance. [Background technology]

[0002] In recent years, small-diameter tires have been developed for use in vehicles with lowered floors to expand interior space. These small-diameter tires have low rotational inertia and light tire weight, and are therefore expected to reduce transportation costs. On the other hand, small-diameter tires are required to have high load capacity. A technology described in Patent Document 1 is known as a conventional tire that addresses this issue. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 122169 Summary of the Invention [Problem to be solved by the invention]

[0004] However, small-diameter tires such as those described above are required to have a high load capacity, which leads to problems such as a deterioration in the tire's wear resistance due to an increase in tire contact pressure, and a deterioration in the tire's wet performance due to a reduction in the tire's contact area.

[0005] Therefore, the present invention has been made in consideration of the above, and has an object to provide a tire that can achieve both wet performance and wear resistance. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the tire of the present invention is a tire having a plurality of circumferential grooves and a plurality of land portions partitioned by the plurality of circumferential grooves, characterized in that the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the total tire width SW [mm] is in the range of 100≦SW≦400, at least one of the plurality of circumferential grooves has a groove shape consisting of wide portions and narrow portions alternately connected, the groove width W1 [mm] of the wide portion is in the range of 0.025≦W1 / SW≦0.070 with respect to the total tire width SW [mm], and the groove width W2 [mm] of the narrow portion is in the range of 0.001≦W2 / SW≦0.024 with respect to the total tire width SW [mm]. Effect of the Invention

[0007] In the tire according to the present invention, the wide portion of the circumferential groove ensures the drainage of the tire ground contact area, improving the wet performance of the tire, and the narrow portion ensures the rigidity of the tire ground contact area, improving the wear resistance of the tire. This has the advantage of achieving both wet performance and wear resistance of the tire. In particular, small-diameter tires with tire outer diameters OD and total tire widths SW in the above ranges are required to have high load capacity, so there is a problem that the wear resistance of the tire deteriorates due to an increase in tire ground contact pressure, and the wet performance of the tire deteriorates due to a decrease in the tire ground contact area. In this respect, by providing such a small-diameter tire with the above configuration, there is an advantage that the wet performance and wear resistance of the tire can be significantly improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing a tread surface of the tire shown in FIG. [Diagram 3] FIG. 3 is an enlarged view showing the circumferential groove of the tire shown in FIG. [Figure 4] FIG. 4 is an enlarged view showing an inner region in the vehicle width direction of the tire shown in FIG. [Diagram 5] FIG. 5 is an enlarged view showing an outer region in the vehicle width direction of the tire shown in FIG. [Figure 6] FIG. 6 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 7] FIG. 7 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 8] FIG. 8 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 9] FIG. 9 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 11] FIG. 11 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 12] FIG. 12 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 13] FIG. 13 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 14] FIG. 14 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 15] FIG. 15 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 16] FIG. 16 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 17] FIG. 17 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 18] FIG. 18 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 19] FIG. 19 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 20] FIG. 20 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 21] FIG. 21 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 22] FIG. 22 is an explanatory diagram showing a modified example of the tire shown in FIG. [Diagram 23]FIG. 23 is an explanatory diagram showing a modified example of the tire shown in FIG. [Figure 24] FIG. 24 is an explanatory diagram showing a modified example of the tire shown in FIG. [Diagram 25] FIG. 25 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. [Figure 26] FIG. 26 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments. The components of the embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. The multiple modified examples described in the embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[0010] [tire] 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction of the tire 1 mounted on a rim 10. In this embodiment, a pneumatic radial tire for passenger cars will be described as an example of a tire.

[0011] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width DW defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis. Point T is the tire ground contact edge, and point Ac is the maximum tire width position.

[0012] The tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, a pair of rim cushion rubbers 17, 17, and an inner liner 18 (see Figure 1).

[0013] The pair of bead cores 11, 11 are formed by winding one or more bead wires made of steel in an annular shape in multiple layers, and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions. The bead filler 12 has a rubber hardness Hs_bf of 55 to 105, a modulus M_bf [MPa] at 100[%] elongation of 2.0 to 13.0, and a loss tangent tanδ_bf of 0.03 to 0.30, and preferably has a rubber hardness Hs_bf of 70 to 100, a modulus M_bf [MPa] at 100[%] elongation of 3.0 to 12.0, and a loss tangent tanδ_bf of 0.05 to 0.25.

[0014] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally stretched between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wound back and secured to the outside in the tire width direction so as to envelop the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of inorganic fibers (e.g., steel, carbon fiber, glass fiber) or organic fibers (e.g., aramid, nylon, polyester, rayon, etc.) with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction with respect to the tire circumferential direction) of 80 degrees or more and 100 degrees or less.

[0015] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is disposed by being wrapped around the outer periphery of the carcass layer 13. In the configuration of FIG. 1, the belt plies 141 to 144 are each composed of a pair of cross belts 141, 142, a belt cover 143, and a pair of belt edge covers 144, 144.

[0016] The pair of cross belts 141, 142 are formed by covering a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 15 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 141, 142 have cord angles of opposite signs to each other, and are layered with the longitudinal directions of the belt cords crossing each other (so-called cross-ply structure). The pair of cross belts 141, 142 are layered and arranged on the outer side of the carcass layer 13 in the tire radial direction.

[0017] The belt cover 143 and the pair of belt edge covers 144, 144 are configured by covering a belt cover cord made of steel or organic fiber material with coating rubber, and have a cord angle of 0 degrees or more and 10 degrees or less in absolute value. The belt cover 143 and the belt edge cover 144 are, for example, strip materials configured by covering one or more belt cover cords with coating rubber, and are configured by winding the strip materials spirally multiple times in the tire circumferential direction around the outer circumferential surfaces of the cross belts 141, 142. The belt cover 143 is disposed to cover the entire area of ​​the cross belts 141, 142, and the pair of belt edge covers 144, 144 are disposed to cover the left and right edge portions of the cross belts 141, 142 from the outside in the tire radial direction.

[0018] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the tire 1. The tread rubber 15 also includes a cap tread 151 and an under tread 152.

[0019] The cap tread 151 is made of a rubber material having excellent ground contact characteristics and weather resistance, and is exposed to the tread surface over the entire tire ground contact area to form the outer surface of the tread portion. The cap tread 151 has a rubber hardness Hs_cap of 50 to 80, a modulus M_cap [MPa] at 100[%] elongation of 1.0 to 4.0, and a loss tangent tanδ_cap of 0.03 to 0.36, and preferably has a rubber hardness Hs_cap of 58 to 76, a modulus M_cap [MPa] at 100[%] elongation of 1.5 to 3.2, and a loss tangent tanδ_cap of 0.06 to 0.29.

[0020] Rubber hardness Hs is measured at a temperature of 20°C in accordance with JIS K6253.

[0021] The modulus (breaking strength) is measured by a tensile test using a dumbbell-shaped test piece at a temperature of 20°C in accordance with JIS K6251 (using No. 3 dumbbell).

[0022] The loss tangent tan δ is measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under the conditions of a temperature of 60°C, a shear strain of 10%, an amplitude of ±0.5%, and a frequency of 20 Hz.

[0023] The undertread 152 is made of a rubber material having excellent heat resistance, and is sandwiched between the cap tread 151 and the belt layer 14 to form a base portion of the tread rubber 15. The undertread 152 has a rubber hardness Hs_ut of 47 to 80, a modulus M_ut [MPa] at 100[%] elongation of 1.4 to 5.5, and a loss tangent tanδ_ut of 0.02 to 0.23, and preferably has a rubber hardness Hs_ut of 50 to 65, a modulus M_ut [MPa] at 100[%] elongation of 1.7 to 3.5, and a loss tangent tanδ_ut of 0.03 to 0.10.

[0024] Moreover, the difference in rubber hardness Hs_cap-Hs_ut is in the range of 3 to 20, and preferably in the range of 5 to 15. The difference in modulus M_cap-M_ut [MPa] is in the range of 0 to 1.4, and preferably in the range of 0.1 to 1.0. The difference in loss tangent tanδ_cap-tanδ_ut is in the range of 0 to 0.22, and preferably in the range of 0.02 to 0.16.

[0025] A pair of sidewall rubbers 16, 16 are disposed on the outer side of the carcass layer 13 in the tire width direction to form left and right sidewall portions. In the configuration of FIG. 1, the outer end of the sidewall rubber 16 in the tire radial direction is disposed in the lower layer of the tread rubber 15 and sandwiched between the end of the belt layer 14 and the carcass layer 13. However, this is not limited thereto, and the outer end of the sidewall rubber 16 in the tire radial direction may be disposed in the outer layer of the tread rubber 15 and exposed to the buttress portion of the tire (not shown). In this case, a belt cushion (not shown) is sandwiched between the end of the belt layer 14 and the carcass layer 13.

[0026] In addition, the sidewall rubber 16 has a rubber hardness Hs_sw of 48 to 65, a modulus M_sw [MPa] at 100% elongation of 1.0 to 2.4, and a loss tangent tanδ_sw of 0.02 to 0.22, and preferably has a rubber hardness Hs_sw of 50 to 59, a modulus M_sw [MPa] at 100% elongation of 1.2 to 2.2, and a loss tangent tanδ_sw of 0.04 to 0.20.

[0027] The pair of rim cushion rubbers 17, 17 extend from the tire radially inner side to the tire widthwise outer side of the turn-up parts of the left and right bead cores 11, 11 and the carcass layer 13 to form the rim fitting surface of the bead part. In the configuration of FIG. 1, the tire radially outer end of the rim cushion rubber 17 is inserted into the lower layer of the sidewall rubber 16 and is sandwiched between the sidewall rubber 16 and the carcass layer 13. The rim cushion rubber 17 has a rubber hardness Hs_rc of 60 to 80, a modulus M_rc [MPa] at 100[%] elongation of 2.0 to 7.0, and a loss tangent tanδ_rc of 0.09 to 0.35, and preferably has a rubber hardness Hs_rc of 65 to 75, a modulus M_rc [MPa] at 100[%] elongation of 3.0 to 6.0, and a loss tangent tanδ_rc of 0.11 to 0.30.

[0028] The inner liner 18 is an air permeation prevention layer disposed on the tire cavity surface and covering the carcass layer 13, suppressing oxidation due to exposure of the carcass layer 13 and preventing leakage of air filled in the tire. The inner liner 18 may be composed of, for example, a rubber composition containing butyl rubber as a main component, or may be composed of a thermoplastic resin or a thermoplastic elastomer composition in which an elastomer component is blended into a thermoplastic resin.

[0029] In FIG. 1, the tire outer diameter OD [mm] is in the range of 200≦OD≦660, and preferably in the range of 250 [mm]≦OD≦580 [mm]. By applying such a small-diameter tire, the effect of improving the load performance described below can be significantly obtained. In addition, the tire total width SW [mm] is in the range of 100≦SW≦400, and preferably in the range of 105 [mm]≦SW≦340 [mm]. With such a small-diameter tire 1, for example, the floor surface of a small vehicle can be lowered to expand the interior space. In addition, since the rotational inertia is small and the tire weight is also small, fuel efficiency is improved and transportation costs are reduced. In particular, when the tire is mounted on an in-wheel motor of a vehicle, the load on the motor is effectively reduced.

[0030] The outer diameter OD of a tire is measured with the tire mounted on a specified rim, pressurized to a specified internal pressure, and under no load.

[0031] The total tire width SW is measured as the straight-line distance between the sidewalls (including all parts such as patterns and lettering on the side of the tire) when the tire is mounted on a specified rim, pressurized to the specified internal pressure, and unloaded.

[0032] The specified rim refers to the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. The specified load refers to the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity.

[0033] Further, the tire total width SW [mm] and the tire outer diameter OD [mm] are in the range of 0.23≦SW / OD≦0.84, and preferably in the range of 0.25≦SW / OD≦0.81.

[0034] It is also preferable that the tire outer diameter OD and the tire total width SW satisfy the following formula (1), where A1min=-0.0017, A2min=0.9, A3min=130, A1max=-0.0019, A2max=1.4, A3max=400, and preferably A1min=-0.0018, A2min=0.9, A3min=160, A1max=-0.0024, A2max=1.6, A3max=362.

[0035]

number

[0036] The tire 1 is assumed to use a rim 10 having a rim diameter of 5 inches to 16 inches (i.e., 125 mm to 407 mm). The rim diameter RD [mm] is in the range of 0.50≦RD / OD≦0.74 with respect to the tire outer diameter OD [mm], and preferably in the range of 0.52≦RD / OD≦0.71. The lower limit ensures that the rim diameter RD is secured, and in particular that the installation space for the in-wheel motor can be secured. The upper limit ensures that the internal volume V of the tire, which will be described later, is secured, and the load capacity of the tire is secured.

[0037] The inner diameter of the tire is equal to the rim diameter RD of the rim 10.

[0038] The tire 1 is expected to be used at an internal pressure higher than the specified internal pressure, specifically, at an internal pressure of 350 kPa to 1200 kPa, preferably 500 kPa to 1000 kPa. The lower limit ensures the load capacity of the tire, and the upper limit ensures the safety of the internal pressure filling operation.

[0039] The tire 1 is assumed to be mounted on a vehicle that travels at a low speed, such as a small shuttle bus. The maximum speed of the vehicle is 100 [km / h] or less, preferably 80 [km / h] or less, and more preferably 60 [km / h] or less. The tire 1 is assumed to be mounted on a vehicle with 6 to 12 wheels. This allows the tire to exhibit its load capacity appropriately.

[0040] The aspect ratio of the tire, that is, the ratio SH / DW of the tire section height SH [mm] to the tire section width DW [mm], is in the range of 0.16≦SH / DW≦0.85, and preferably in the range of 0.19≦SH / DW≦0.82.

[0041] The tire section height SH is half the distance between the tire outer diameter and the rim diameter, and is measured with the tire mounted on a specified rim, with a specified internal pressure applied, and in an unloaded state.

[0042] The tire section width DW is measured as the straight-line distance between the sidewalls (excluding any patterns or lettering on the side of the tire) when the tire is mounted on a specified rim, pressurized to the specified internal pressure, and unloaded.

[0043] Further, the tire contact width TW is in the range of 0.50≦TW / SW≦0.85 relative to the tire total width SW, and preferably in the range of 0.60≦TW / SW≦0.80.

[0044] The tire contact width TW is measured as the maximum straight-line distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0045] Furthermore, the tire internal volume V [m^3] is in the range of 4.0≦(V / OD)×10^6≦60, preferably 6.0≦(V / OD)×10^6≦50, relative to the tire outer diameter OD [mm]. This optimizes the tire internal volume V. Specifically, the lower limit ensures the tire internal volume and the tire's load capacity. In particular, small-diameter tires are expected to be used under high internal pressure and high load, so it is preferable that the tire internal volume V is sufficiently ensured. The upper limit prevents the tire from becoming too large due to the tire internal volume V being too large.

[0046] Further, the tire internal volume V [m^3] is in the range of 0.5≦V×RD≦17 relative to the rim diameter RD [mm], and preferably in the range of 1.0≦V×RD≦15.

[0047] [Carcass layer] 1, as described above, the carcass layer 13 is made of a single carcass ply and is disposed in a toroidal shape spanning between the left and right bead cores 11, 11. In addition, both ends of the carcass layer 13 are wrapped back and secured to the outside in the tire width direction so as to encase the bead cores 11 and the bead fillers 12.

[0048] In addition, the strength Tcs [N / 50mm] per 50 [mm] of the width of the carcass ply constituting the carcass layer 13 is in the range of 17≦Tcs / OD≦120 with respect to the tire outer diameter OD [mm], and preferably in the range of 20≦Tcs / OD≦120. In addition, the strength Tcs [N / 50mm] of the carcass layer 13 is in the range of 30≦Tcs / SW≦260 with respect to the tire total width SW [mm], and preferably in the range of 35≦Tcs / SW≦220. In this configuration, the load capacity of the carcass layer 13 is appropriately ensured in a small diameter tire, so that the tire has both durability and low rolling resistance. Specifically, the above lower limit suppresses tire deformation during use under high load, and ensures durability of the tire. In addition, use at high internal pressure is possible, and the rolling resistance of the tire is reduced. In particular, in small-diameter tires, which are expected to be used under high internal pressure and high load, the tire durability and rolling resistance reduction effects described above are significantly achieved. The above upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the carcass layer.

[0049] The strength Tcs [N / 50mm] of the carcass ply is calculated as follows. That is, the carcass ply that is stretched across the left and right bead cores 11, 11 and extends over the entire inner circumference of the tire is defined as the effective carcass ply. The strength Tcs [N / 50mm] of the carcass ply is calculated as the product of the strength [N / cord] of each carcass cord constituting the effective carcass ply and the number of carcass cords [cords / 50mm] per width of 50 [mm] on the entire circumference of the tire and on the tire equatorial plane CL. The strength of the carcass cord is measured by a tensile test at a temperature of 20 [°C] in accordance with JIS K1017. For example, in a configuration in which one carcass cord is formed by twisting a plurality of wires, the strength of one twisted carcass cord is measured, and the strength Tcs of the carcass layer 13 is calculated. In addition, in a configuration in which the carcass layer 13 has a multi-layer structure (not shown) formed by laminating a plurality of effective carcass plies, the above-mentioned strength Tcs is defined for each of the plurality of effective carcass plies.

[0050] For example, in the configuration of Fig. 1, the carcass layer 13 has a single layer structure made of a single carcass ply (reference numerals omitted in the figure), and the carcass ply is configured by arranging carcass cords made of steel covered with a coating rubber at a cord angle of 80 degrees or more and 100 degrees or less with respect to the tire circumferential direction (not shown). The carcass cords made of steel have a cord diameter φcs [mm] in the range of 0.15 ≦ φcs ≦ 1.10, preferably 0.25 ≦ φcs ≦ 0.60, and an end count Ecs [pieces / 50mm] in the range of 25 ≦ Ecs ≦ 80, preferably 50 ≦ Ecs ≦ 80, thereby realizing the strength Tcs [N / 50mm] of the carcass layer 13 described above. The carcass cords are formed by twisting a plurality of wires together, and the wire diameter φcss [mm] is in the range of 0.12 ≦ φcss ≦ 0.24, preferably 0.14 ≦ φcss ≦ 0.22. It is more preferable that the wire diameter φcss [mm] of the carcass cord is in the range of 0.30≦φcss / φcs≦0.90 with respect to the cord diameter φcs [mm] of the carcass cord. The carcass cord may be made of inorganic fibers other than steel (e.g., carbon fiber, glass fiber, etc.).

[0051] Furthermore, without being limited to the above, the carcass ply may be constituted by a carcass cord made of an organic fiber material (such as aramid, nylon, polyester, rayon, etc.) covered with a coating rubber. In this case, the carcass cord made of the organic fiber material has a cord diameter φcs [mm] in the range of 0.60≦φcs≦0.90 and an end count Ecs [pieces / 50 mm] in the range of 40≦Ecs≦70, thereby realizing the strength Tcs [N / 50 mm] of the carcass layer 13 described above. In addition, carcass cords made of organic fiber materials such as high-strength nylon, aramid, and hybrids can be adopted within the scope of obviousness to those skilled in the art.

[0052] Furthermore, the carcass layer 13 may have a multi-layer structure (not shown) formed by laminating a plurality of carcass plies, for example, two carcass plies, which can effectively increase the load carrying capacity of the tire.

[0053] Moreover, the total strength TTcs [N] of the carcass layer 13 is in the range of 300≦TTcs / OD≦3500, and preferably in the range of 400≦TTcs / OD≦3000, relative to the tire outer diameter OD [mm]. This ensures the overall load capacity of the carcass layer 13.

[0054] The total strength TTcs [N] of the carcass layer 13 is calculated as the product of the strength per carcass cord [N / cord] and the total number of carcass cords in the entire carcass layer 13. Therefore, the total strength TTcs [N] of the carcass layer 13 increases with an increase in the strength Tcs [N / 50mm] of each carcass ply, the number of carcass plies laminated, the circumferential length of the carcass ply, etc.

[0055] It is also preferable that the total strength TTcs [N] of the carcass layer 13 satisfies the following formula (4) with respect to the tire outer diameter OD [mm] and the distance SWD [mm], where Dmin=2.2, Dmax=40, preferably Dmin=4.3, Dmax=40, more preferably Dmin=6.5, Dmax=40, and even more preferably Dmin=8.7, Dmax=40. Furthermore, it is preferable that Dmin=0.02×P, where P [kPa] is the specified tire internal pressure.

[0056]

number

[0057] [Tread surface] FIG. 2 is a plan view showing the tread surface of the tire 1 shown in FIG. 1. The figure shows, as an example, the tread surface of a small-diameter tire that satisfies the above-mentioned conditions of the outer diameter OD and total width SW. FIG. 3 is an enlarged view showing the circumferential grooves 21, 22 of the tire 1 shown in FIG. 2. FIG. 4 is an enlarged view showing the inner region in the vehicle width direction of the tire 1 shown in FIG. 2. FIG. 5 is an enlarged view showing the outer region in the vehicle width direction of the tire 1 shown in FIG. 2. In these figures, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T is the tire ground contact end, and the dimension symbol TW is the tire ground contact width.

[0058] In addition, in FIG. 2, the vehicle width direction inner side and the vehicle width direction outer side are defined as the directions relative to the vehicle width direction when the tire is mounted on a vehicle. The left and right regions bounded by the tire equatorial plane CL are defined as the vehicle width direction outer region and the vehicle width direction inner region, respectively. The tire is equipped with a mounting direction indicator (not shown) that indicates the tire mounting direction on the vehicle. The mounting direction indicator is configured, for example, by a mark or unevenness provided on the sidewall portion of the tire. For example, ECER30 (Article 30 of the Economic Commission for Europe Regulation) requires that a vehicle mounting direction indicator be provided on the sidewall portion that is on the vehicle width direction outer side when mounted on the vehicle.

[0059] As shown in FIG. 2, the tire 1 includes first and second circumferential grooves 21, 22, a pair of shoulder land portions 31, 32, and a single center land portion 33 on the tread surface.

[0060] The first and second circumferential grooves 21, 22 are grooves that contribute to drainage performance, and have an annular structure that extends continuously over the entire circumference in the tire circumferential direction.

[0061] For example, in the configuration of FIG. 2, the first and second circumferential grooves 21, 22 are main grooves that are required to display a wear indicator as stipulated by JATMA, and have a maximum groove width of 3.0 mm or more and a maximum groove depth of 5.0 mm or more in wide portions 211, 221 described later. The first and second circumferential grooves 21, 22 are disposed in left and right regions bounded by the tire equatorial plane CL, respectively. Specifically, the first circumferential groove 21 is disposed in an inner region in the vehicle width direction, and the second circumferential groove 22 is disposed in an outer region in the vehicle width direction. The tire 1 does not include any other circumferential grooves.

[0062] However, the present invention is not limited to this and the tire 1 may have three or more circumferential grooves (see Figs. 14 and 15 described later). In this case, it is preferable that the number G of circumferential grooves is in the range of 0.010≦G / SW≦0.025 with respect to the total tire width SW [mm]. For example, in a test tire having a tire size of 145 / 80R12 described later, it is preferable that the number G of circumferential grooves is two or three.

[0063] 2, each of the circumferential grooves 21 and 22 has a groove shape in which wide portions 211 and 221 and narrow portions 212 and 222 are alternately connected. Therefore, the groove widths of the circumferential grooves 21 and 22 periodically increase and decrease in the tire circumferential direction. The wide portions 211 and 221 and the narrow portions 212 and 222 are defined as portions having the following groove widths W1 and W2.

[0064] That is, in FIG. 3, the groove width W1 [mm] of the wide portions 211 and 221 is in the range of 0.025 ≦ W1 / SW ≦ 0.070 with respect to the total tire width SW [mm], preferably in the range of 0.025 ≦ W1 / SW ≦ 0.055. Also, the groove width W2 [mm] of the narrow portions 212 and 222 has a relationship of W2 < W1 with respect to the groove width W1 [mm] of the wide portions 211 and 221. Specifically, the groove width W2 [mm] of the narrow portions 212 and 222 is in the range of 0.001 ≦ W2 / SW ≦ 0.024 with respect to the total tire width SW [mm], preferably in the range of 0.005 ≦ W2 / SW ≦ 0.024. Therefore, the boundary between the wide portions 211;221 and the narrow portions 212;222 is at the position where the groove width of the circumferential grooves 21;22 becomes 0.025 times the total tire width SW [mm]. Also, regardless of the tire size, it is preferable that the groove width W1 [mm] of the wide portions 211 and 221 is in the range of 5.0 < W1, and the groove width W2 [mm] of the narrow portions 212 and 222 is in the range of W2 < 8.0.

[0065] The groove width is measured as the distance between the opposing groove walls at the groove opening on the tread surface in the unloaded state where the tire is mounted on a specified rim and filled with a specified internal pressure. In a configuration having a notch or a chamfer at the groove opening, the groove width is measured with the intersection of the extension line of the tread surface and the extension line of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction as an end point.

[0066] In the above configuration, the drainage performance of the tire contact area is ensured by the wide portions 211 and 221 of the circumferential grooves 21 and 22, improving the wet performance of the tire, and the rigidity of the tire contact area is ensured by the narrow portions 212 and 222, improving the wear resistance of the tire. Thereby, the wet performance and the wear resistance performance of the tire are made compatible. In particular, in the case of a small-diameter tire where the tire outer diameter OD and the total tire width SW are in the above ranges, since a high load capacity is required, there is a problem that the wear resistance performance of the tire deteriorates due to an increase in the tire contact pressure, and the wet performance of the tire deteriorates due to a decrease in the tire contact area. In this regard, when such a small-diameter tire has the above configuration, the improvement effect on the wet performance and the wear resistance performance of the tire can be remarkably obtained.

[0067] 3, the minimum value _min of the groove width W2 [mm] of the narrow width portions 212, 222 is in the range of 0.10≦W2_min / W1_max≦0.50, and preferably in the range of 0.20≦W2_min / W1_max≦0.40, relative to the maximum value of the groove width W1_max [mm] of the wide width portions 211, 221. The lower limit ensures the wet performance of the tire, and the upper limit ensures the wear resistance of the tire.

[0068] In addition, the groove depth H1 [mm] (not shown) of the wide portions 211, 221 is in the range of 0.008≦H1 / OD≦0.030 relative to the tire outer diameter OD [mm], and the groove depth H2 [mm] (not shown) of the narrow portions 212, 222 is in the range of 0.005≦H2 / OD≦0.020 relative to the tire outer diameter OD [mm].

[0069] The groove depth is measured as the distance from the tread surface to the bottom of the groove when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In the case of a tire having partial unevenness or sipes at the bottom of the groove, the groove depth is measured excluding these.

[0070] Also, in FIG. 3, the perimeter L1 [mm] of the wide portions 211 and 221 is in the range of 0.025 ≦ L1 / OD ≦ 0.065 with respect to the tire outer diameter OD [mm], and preferably in the range of 0.030 ≦ L1 / OD ≦ 0.060. Further, the perimeter L1 [mm] of the wide portions 211 and 221 is in the range of 0.50 ≦ L1 / P2 ≦ 0.85 with respect to the pitch length P2 [mm] of the circumferential grooves 21 and 22, and preferably in the range of 0.51 ≦ L1 / P2 ≦ 0.80. Therefore, the perimeter L2 [mm] of the narrow portions 212 and 222 is preferably shorter than the perimeter L1 [mm] of the wide portions 211 and 221 (L2 < L1), and is in the range of 0.015 ≦ L2 / OD ≦ 0.055 with respect to the tire outer diameter OD [mm], and more preferably in the range of 0.020 ≦ L2 / OD ≦ 0.050. By the above lower limit of the perimeter L1 of the wide portions 211 and 221 and the above upper limit of the perimeter L2 of the narrow portions 212 and 222, the wet performance of the tire is ensured, and by the above upper limit of the perimeter L1 of the wide portions 211 and 221 and the above lower limit of the perimeter L2 of the narrow portions 212 and 222, the wear resistance performance of the tire is ensured. Note that it is only necessary for the perimeter L1 included in any pitch length P2 to satisfy the above ratio L1 / P2 condition.

[0071] The perimeters L1 and L2 are calculated as the average value of the lengths extending in the tire circumferential direction of the wide portions 211 and 221 or the narrow portions 212 and 222 on the tread surface in a no-load state where the tire is mounted on a specified rim and filled with a specified internal pressure.

[0072] Also, in FIG. 3, the pitch length P2 of the circumferential grooves 21 and 22 is in the range of 0.20 ≦ P2 / LA ≦ 0.60 with respect to the tire contact length LA [mm] (not shown), and preferably in the range of 0.25 ≦ P2 / LA ≦ 0.55. More preferably, the perimeters L1 [mm] of the wide portions 211 and 221 and the perimeter L2 [mm] of the narrow portions 212 and 222 satisfy the condition of L1 + L1 + L2 ≦ LA or L1 + L2 + L2 ≦ LA with respect to the tire contact length LA [mm]. Thereby, the wet performance and the wear resistance performance of the tire are efficiently compatible.

[0073] The tire contact length LA is measured as the maximum straight-line distance in the tire circumferential direction at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0074] For example, in the configuration of Fig. 3, the groove openings of the circumferential grooves 21, 22 have rectangular or trapezoidal wave-shaped edges having a straight shape at the maximum amplitude position, and the left and right edges of the groove openings are arranged with their phases inverted by 180[deg] from each other. As a result, the groove width of each of the circumferential grooves 21, 22 increases and decreases periodically in the tire circumferential direction, and the groove openings of the circumferential grooves 21, 22 have straight and parallel edges at the maximum and minimum positions of the groove width of the circumferential grooves 21, 22. It is preferable that the groove width W1 of the wide portions 211, 221 is maximum in an area of ​​60[%] or more, preferably 80[%] or more of the circumferential length L1 of the wide portions 211, 221, and that the groove width W2 of the narrow portions 212, 222 is minimum in an area of ​​60[%] or more, preferably 80[%] or more of the circumferential length L2 of the narrow portions 212, 222. However, the present invention is not limited thereto, and the left and right edge portions of each of the circumferential grooves 21, 22 may have, for example, a sinusoidal shape (not shown). Also, only one edge portion of each of the circumferential grooves 21, 22 may have a wavy shape, and the other edge portion may have a straight shape (not shown).

[0075] As shown in Fig. 2, the first circumferential groove 21 and the second circumferential groove 22 are arranged with a phase shift in the tire circumferential direction, so that the wide portion 211 of the first circumferential groove 21 and the wide portion 221 of the second circumferential groove 22 are arranged in a staggered manner in the tire circumferential direction. Specifically, in Fig. 3, the phase difference φ2 [mm] between the first circumferential groove 21 and the second circumferential groove 22 is in the range of 0.20 ≦ φ2 / P2 ≦ 0.80 with respect to the pitch length P2 [mm] of the circumferential grooves 21 and 22, and preferably in the range of 0.30 ≦ φ2 / P2 ≦ 0.70. This improves the drainage in the tread center region, improving the wet performance of the tire, and also uniforms the rigidity in the tire circumferential direction in the tread center region, improving the wear resistance of the tire.

[0076] 3, the wide portions 211, 221 of the first and second circumferential grooves 21, 22 have the same groove widths W1, W1 and circumferential lengths L1, L1, and the narrow portions 212, 222 have the same groove widths W2, W2 and circumferential lengths L2, L2. However, this is not limiting, and as described later, the wide portions 211, 221 and the narrow portions 212, 222 of the first and second circumferential grooves 21, 22 may have different groove widths and circumferential lengths.

[0077] 2, the groove width W2' [mm] (not shown) of the narrow width portions 212, 222 when the tire 1 is mounted on a specified rim, a specified internal pressure is applied, and a specified load is applied, and the groove width W2 [mm] of the narrow width portions 212, 222 when no load is applied are in the range of -15≦|W2'-W2| / W2×100-RL≦+15 with respect to the load load rate RL [%] when the specified load is applied, and preferably in the range of -10≦|W2'-W2| / W2×100-RL≦+10. As a result, the rate of change of the groove width W2' of the narrow width portions 212, 222 is approximately proportional to the load load rate RL [%], and the wet performance and wear resistance of the tire are effectively compatible.

[0078] The load factor RL is calculated as the ratio between the above-mentioned predetermined load and the maximum load capacity at the specified internal pressure described in JATMA.

[0079] In addition, in Fig. 2, a pair of circumferential grooves arranged on the outermost sides in the tire width direction and alternately connecting the wide and narrow portions described above are called shoulder circumferential grooves. In the configuration in Fig. 2, two circumferential grooves 21, 22 are arranged in the inner and outer regions in the vehicle width direction bounded by the tire equatorial plane CL, and these are shoulder circumferential grooves. In addition, as described later, in a configuration in which three or more circumferential grooves are arranged, shoulder circumferential grooves are defined in the inner and outer regions in the vehicle width direction, respectively.

[0080] In addition, a circumferential groove that is disposed in a position closest to the tire equatorial plane CL in the vehicle width direction inner region and that alternately connects the wide and narrow portions is called a center circumferential groove. In a configuration in which a single circumferential groove 21 is disposed in the vehicle width direction inner region as shown in Fig. 2, this circumferential groove 21 serves as both a center circumferential groove and a shoulder circumferential groove.

[0081] At this time, the distance G1W [mm] from the tire equatorial plane CL to the center circumferential groove 21 in the one vehicle width direction inner region is in the range of 0.20 ≦ G1W / G2W ≦ 0.85 with respect to the distance G2W [mm] from the tire equatorial plane CL to the shoulder circumferential groove 22 in the vehicle width direction outer region, and is preferably in the range of 0.25 ≦ G1W / G2W ≦ 0.80. In addition, the distance G1W [mm] and the distance G2W [mm] are in the ranges of 0.01 ≦ G1W / TW ≦ 0.30 and 0.10 ≦ G2W / TW ≦ 0.40 with respect to the tire ground contact width TW [mm], and are preferably in the ranges of 0.05 ≦ G1W / TW ≦ 0.25 and 0.15 ≦ G2W / TW ≦ 0.35. This improves the wear resistance and drainage performance of the tire.

[0082] The distance G1W of the center circumferential groove 21 and the distance G2W of the shoulder circumferential groove 22 are measured as the distance from the tire equatorial plane CL to the groove center line of each circumferential groove 21, 22 when the tire is mounted on a specified rim, a specified internal pressure is applied, and the tire is in an unloaded state.

[0083] The groove centerline is defined as an imaginary line connecting the midpoints of the distance between opposing groove walls.

[0084] 2, the sum ΣSc [mm^2] of the groove areas Sc1 and Sc2 of the circumferential grooves 21 and 22 in the tire ground contact region is in the range of 0.60≦(ΣSc) / Sa≦1.00 with respect to the groove area Sa [mm^2] of the tire ground contact region, and preferably in the range of 0.65≦(ΣSc) / Sa≦0.95. The sum ΣVc of the groove volumes [mm^3] of the circumferential grooves 21 and 22 in the tire ground contact region is in the range of 0.70≦(ΣVc) / Va≦1.00 with respect to the groove volume Va [mm^3] of the tire ground contact region, and preferably in the range of 0.75≦(ΣVc) / Va≦0.99. This ensures the drainage of the tread center region by the circumferential grooves 21 and 22, and also suppresses the decrease in rigidity of the land portions 31 and 32 caused by the excessive groove areas of the lug grooves 311, 312, 321, and 322 described later.

[0085] The groove area is the opening area of ​​the groove on the tread surface, and is measured at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, a specified internal pressure is applied, the tire is placed perpendicular to a flat plate in a stationary state, and a load corresponding to a specified load is applied.

[0086] In addition, the sum ΣSc [mm^2] of the groove areas Sc1, Sc2 of the circumferential grooves 21, 22 in the tire ground contact region is in the range of 0.01≦(ΣSc) / Sr≦0.15, preferably 0.02≦(ΣSc) / Sr≦0.13, relative to the area Sr [mm^2] of the tire ground contact region. The lower limit ensures drainage in the tread center region, and the upper limit ensures rigidity in the tread center region.

[0087] In addition, the groove area ratio [%] of the tire ground contact region is in the range of 1 [%] to 16 [%], preferably in the range of 2 [%] to 15 [%]. This ensures the wet performance and wear resistance of the tire. In addition, it is preferable that the groove area [mm^2] on the inner side in the vehicle width direction, which is bounded by the tire equatorial plane CL, is larger than the groove area [mm^2] on the outer side in the vehicle width direction. In addition, it is preferable that the groove volume [mm^3] on the inner side in the vehicle width direction, which is bounded by the tire equatorial plane CL, is smaller than the groove volume [mm^2] on the outer side in the vehicle width direction. This ensures the drainage of the tire ground contact region, and also suppresses a decrease in the rigidity of the tire ground contact region.

[0088] The groove area ratio of a tire contact area is defined as the ratio of the area of ​​that area to the sum of the areas of grooves arranged in a given area.

[0089] In FIG. 2, a pair of shoulder land portions 31, 32 and a single center land portion 33 are defined by the circumferential grooves 21, 22.

[0090] Each of the shoulder land portions 31;32 includes a plurality of lug grooves 311, 312;321 extending in the tire width direction. Furthermore, one end of each of these lug grooves 311, 312;321 extends beyond the tire ground contact edge T to the buttress portion, and the other end terminates in the ground contact region of the shoulder land portion 31;32. Therefore, each of the shoulder land portions 31;32 is a rib having a tread surface that is continuous in the tire circumferential direction.

[0091] The tire ground contact edge T is defined as the widest position in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0092] For example, in the configuration of FIG. 2, the shoulder land portion 31 in the vehicle width direction inner region has first and second lug grooves 311, 312, and these lug grooves 311, 312 are arranged alternately in the tire circumferential direction. Also, as shown in FIG. 4, the first and second lug grooves 311, 312 have a straight shape or a gentle arc shape, and are inclined at predetermined inclination angles θ311, θ312 with respect to the tire width direction. Also, the first and second lug grooves 311, 312 are inclined in mutually different directions with respect to the tire width direction. Also, the inclination angles θ311, θ312 of the first and second lug grooves 311, 312 are in the range of 10 [deg] or more and 20 [deg] or less. This ensures the drainage of the first and second lug grooves 311, 312.

[0093] The inclination angles θ311, θ312 of the lug grooves 311, 312 are measured as angles between an imaginary line connecting both ends of the lug grooves 311, 312 and the tire width direction.

[0094] 4, it is preferable that the groove widths W311, W312 of the first and second lug grooves 311, 312 are equal to or smaller than the groove width W1 of the wide portion 211 of the circumferential groove 21 and equal to or larger than the groove width W2 of the narrow portion 212. It is also preferable that the groove depths (not shown) of the first and second lug grooves 311, 312 are equal to or larger than 20[%] and equal to or smaller than 50[%] of the groove depth of the wide portion 211 of the circumferential groove 21. This can improve the wet performance of the tire while ensuring the pattern rigidity.

[0095] 4, the distance R1W [mm] in the tire width direction from the tire equatorial plane CL to the ends of the first and second lug grooves 311, 312 is in the range of 0.20≦R1W / TW≦0.50, preferably 0.25_≦R1W / TW≦0.45, relative to the tire ground contact width TW (see FIG. 2). However, as described above, the ends of the first and second lug grooves 311, 312 must be spaced outward in the tire width direction relative to the circumferential groove 21. This can improve the tire's wear resistance and wet performance while ensuring the pattern rigidity.

[0096] In the configuration of FIG. 2, the shoulder land portion 32 in the vehicle width direction outer region has a lug groove 321. The number of lug grooves 321 in the vehicle width direction outer region is smaller than the number of first and second lug grooves 311, 312 in the vehicle width direction inner region, and is 1 / 2 in the configuration of FIG. 2. As shown in FIG. 5, the lug groove 321 has a straight line shape or a gentle arc shape and is inclined at a predetermined inclination angle θ321 with respect to the tire width direction. The inclination angle θ321 [deg] of the lug groove 321 in the vehicle width direction outer region is smaller than the inclination angles θ311, θ312 [deg] of the first and second lug grooves 311, 312 in the vehicle width direction inner region, and is preferably in the range of 0≦θ321≦8. In the configuration of FIG. 5, the lug groove 321 of the shoulder land portion 32 in the vehicle width direction outer region has a straight line shape parallel to the tire width direction. This makes it possible to improve the wear resistance and wet performance of the tire while ensuring the pattern rigidity.

[0097] 5, it is preferable that the groove width W321 of the lug groove 321 is equal to or smaller than the groove width W1 of the wide portion 211 of the circumferential groove 21 and equal to or larger than the groove width W2 of the narrow portion 212. It is also preferable that the groove depth (not shown) of the lug groove 321 is equal to or larger than 20[%] and equal to or smaller than 50[%] of the groove depth of the wide portion 211 of the circumferential groove 21. This can improve the wet performance of the tire while ensuring the pattern rigidity.

[0098] 5, the distance R2W [mm] in the tire width direction from the tire equatorial plane CL to the end of the lug groove 321 is in the range of 0.35≦R2W / TW≦0.65 with respect to the tire ground contact width TW (see FIG. 2), and preferably in the range of 0.40≦R2W / TW≦0.60. However, as described above, it is necessary that the end of the lug groove 321 is spaced outward in the tire width direction from the circumferential groove 22. This can improve the wear resistance and wet performance of the tire while ensuring the pattern rigidity.

[0099] [Variations] Figures 6 to 24 are explanatory diagrams showing modified examples of the tire 1 shown in Figure 2. In these figures, the same components as those shown in Figure 2 are denoted by the same reference numerals, and the description thereof will be omitted.

[0100] In the configuration of Fig. 2, as described above, the shoulder land portion 31 in the vehicle width direction inner region has the first and second lug grooves 311, 312 inclined in mutually different directions with respect to the tire width direction, and the shoulder land portion 32 in the vehicle width direction outer region has the lug groove 321 extending parallel to the tire width direction. Also, the number of the first and second lug grooves 311, 312 in the vehicle width direction inner region is greater than the number of the lug grooves 321 in the vehicle width direction outer region. This configuration is preferable in that the drainage of the vehicle width direction inner region is improved to ensure the wet performance of the tire, and the rigidity of the vehicle width direction outer region is ensured to ensure the wear resistance of the tire.

[0101] In contrast, in the configurations of Fig. 6 and Fig. 7, both the shoulder land portion 31 in the vehicle width direction inner region and the shoulder land portion 32 in the vehicle width direction outer region have lug grooves 311; 321 extending parallel to the tire width direction. The number of lug grooves 311 in the vehicle width direction inner region is set to be the same as the number of lug grooves 321 in the vehicle width direction outer region. In addition, in the configuration of Fig. 6, the lug grooves 311 in the vehicle width direction inner region and the lug grooves 321 in the vehicle width direction outer region are at the same position in the tire circumferential direction and are arranged with the phases aligned with each other. In contrast, in the configuration of Fig. 7, the lug grooves 311 in the vehicle width direction inner region and the lug grooves 321 in the vehicle width direction outer region are offset from each other in the tire circumferential direction, i.e., arranged in a staggered pattern, and arranged with a phase difference (dimension symbols in the figures omitted).

[0102] 8, the shoulder land portion 31 in the vehicle width direction inner region and the shoulder land portion 32 in the vehicle width direction outer region both have first and second lug grooves 311, 312; 321, 322 that are inclined in different directions relative to the tire width direction. The lug grooves 311, 312 in the vehicle width direction inner region and the lug grooves 321, 322 in the vehicle width direction outer region are arranged symmetrically with respect to the tire equatorial plane CL.

[0103] 2, as described above, the number of the first and second lug grooves 311, 312 in the vehicle width direction inner region is greater than the number of the lug grooves 321 in the vehicle width direction outer region, specifically set to twice as many. This configuration is preferable in that the drainage performance in the vehicle width direction inner region is improved to ensure the wet performance of the tire, and the rigidity in the vehicle width direction outer region is ensured to ensure the wear resistance of the tire.

[0104] 9, the number of lug grooves 321 in the vehicle width direction outer region is set to be equal to the number of first and second lug grooves 311, 312 in the vehicle width direction inner region. Meanwhile, the groove width W321 (see FIG. 5) of the lug groove 321 in the vehicle width direction outer region is narrower than the groove widths W311, W312 of the first and second lug grooves 311, 312 in the vehicle width direction inner region. This ensures the rigidity of the vehicle width direction outer region and the wear resistance of the tire.

[0105] In the configuration of FIG. 2, as described above, the shoulder land portion 31 in the vehicle width direction inner region includes the first and second lug grooves 311, 312 inclined in directions different from each other with respect to the tire width direction.

[0106] 10, the shoulder land portion 31 in the vehicle width direction inner region has first and second lug grooves 311, 312 that are inclined in the same direction relative to the tire width direction. The first and second lug grooves 311, 312 are arranged such that the wide portion 211 of the circumferential groove 21 is located on an extension line (not shown) of a pair of adjacent lug grooves 311, 312, while the narrow portion 212 of the circumferential groove 21 is offset from the extension line of the pair of adjacent lug grooves 311, 312.

[0107] In the configuration of FIG. 2, the shoulder land portion 31 in the vehicle width direction inner region is provided with first and second lug grooves 311, 312 having a straight shape.

[0108] 11, the shoulder land portion 31 in the vehicle width direction inner region has arc-shaped first and second lug grooves 311, 312. In this manner, the lug grooves 311, 312 may have a curved shape.

[0109] 2, as described above, the shoulder land portion 31 in the vehicle width direction inner region includes the first and second lug grooves 311, 312 that are inclined in different directions from each other with respect to the tire width direction. The first and second lug grooves 311, 312 are arranged such that the wide portion 211 of the circumferential groove 21 is located on an extension line (not shown) of a pair of adjacent lug grooves 311, 312, while the narrow portion 212 of the circumferential groove 21 is offset from the extension line of the pair of adjacent lug grooves 311, 312.

[0110] In contrast, in the configuration of Figure 12, the first and second lug grooves 311, 312 are arranged so that the narrow portion 212 of the circumferential groove 21 is located on an extension line (not shown) of a pair of adjacent lug grooves 311, 312, while the wide portion 211 of the circumferential groove 21 is offset from the extension line of the pair of adjacent lug grooves 311, 312.

[0111] In the configuration of FIG. 2, as described above, the shoulder land portion 32 in the outer region in the vehicle width direction includes the lug grooves 321 extending parallel to the tire width direction.

[0112] In contrast, in the configuration of Fig. 13, the shoulder land portion 32 in the vehicle width direction outer region has lug grooves 321 inclined in one direction with respect to each other in the tire width direction. In this case, it is preferable that the inclination angle θ321 [deg] (see Fig. 5) of the lug groove 321 in the vehicle width direction outer region is smaller than the inclination angles θ311, θ312 [deg] (see Fig. 4) of the first and second lug grooves 311, 312 in the vehicle width direction inner region. This ensures the pattern rigidity of the vehicle width direction outer region and the wear resistance of the tire.

[0113] Also, in the configuration of FIG. 2, as described above, the tire 1 is provided with two circumferential grooves 21 and 22, and these circumferential grooves 21 and 22 are respectively arranged in the inner and outer regions in the vehicle width direction with the tire equatorial plane CL as the boundary. Further, these circumferential grooves 21 and 22 are arranged at a distance from the tire equatorial plane CL. Such a configuration is preferable in that the rigidity of the tread center region is ensured and the wear resistance performance of the tire is improved.

[0114] On the other hand, in the configurations of FIGS. 14 and 15, the tire 1 is provided with three circumferential grooves 21, 22, and 23. Also, in the configuration of FIG. 14, two circumferential grooves 21 and 23 are arranged on the inner side in the vehicle width direction with the tire equatorial plane CL as the boundary, and one circumferential groove 22 is arranged in the outer region in the vehicle width direction. Further, these circumferential grooves 21, 22, and 23 are arranged at a distance from the tire equatorial plane CL. In such a configuration, the drainage performance in the inner region in the vehicle width direction is improved and the wet performance of the tire is ensured, and also the rigidity in the outer region in the vehicle width direction is ensured and the wear resistance performance of the tire is ensured. On the other hand, in the configuration of FIG. 15, one circumferential groove 21 is arranged on the inner side in the vehicle width direction with the tire equatorial plane CL as the boundary, and two circumferential grooves 22 and 23 are arranged in the outer region in the vehicle width direction. Such a configuration is also acceptable.

[0115] Also, in the configuration of FIG. 2, as described above, the circumferential grooves 21; 22 have a structure in which the wide portions 211; 221 and the narrow portions 212; 222 are alternately connected in the tire circumferential direction. Further, the circumferential length L2 [mm] (see FIG. 3) of the narrow portions 212 and 222 is set shorter than the circumferential length L1 [mm] of the wide portions 211 and 221 (L2 < L1). In such a configuration, the drainage action of the circumferential grooves 21 and 22 is ensured, and it is preferable in that the wet performance of the tire is improved.

[0116] On the other hand, in the configuration of FIG. 16, the circumferential length L2 [mm] (see FIG. 3) of the narrow portions 212 and 222 is set longer than the circumferential length L1 [mm] of the wide portions 211 and 221 (L1 < L2). In such a configuration, the rigidity of the tread center region is ensured, and it is preferable in that the wear resistance performance of the tire is improved.

[0117] In addition, in the configuration of FIG. 2, as described above, the first and second circumferential grooves 21, 22 have a structure in which the wide portions 211, 221 and the narrow portions 212, 222 are alternately connected in the tire circumferential direction. In addition, the first circumferential groove 21 and the second circumferential groove 22 are arranged with a phase shift in the tire circumferential direction, so that the wide portions 211 of the first circumferential groove 21 and the wide portions 221 of the second circumferential groove 22 are arranged in a staggered manner in the tire circumferential direction. In addition, the phase difference φ2 [mm] (see FIG. 3) between the first circumferential groove 21 and the second circumferential groove 22 is set to about 50 [%] with respect to the pitch length P2 [mm] of the circumferential grooves 21, 22. This configuration is preferable in that the rigidity in the tire circumferential direction in the tread center region is uniformized, improving the wear resistance of the tire.

[0118] In contrast, in the configurations of Figures 17 and 18, the phase difference φ2 [mm] (see Figure 3) between the first circumferential groove 21 and the second circumferential groove 22 is set small, so that the wide portion 211 of the first circumferential groove 21 and the wide portion 221 of the second circumferential groove 22 are arranged to overlap each other when projected in the tire width direction.

[0119] In the configuration of FIG. 2, as described above, the pitch length P2 (see FIG. 3) of the circumferential grooves 21, 22 is shorter than the tire contact length LA [mm] (not shown), and the ratio P2 / LA is set in the range of 0.20 to 0.60.

[0120] In contrast, in the configuration of Figure 19, the ratio P2 / LA of the pitch length P2 (see Figure 3) of the circumferential grooves 21, 22 to the tire contact length LA [mm] (not shown) is in the range of 1.00 to 0.60, and in the configuration of Figure 20, the ratio P2 / LA is in the range of 0.05 to 0.20.

[0121] In the configuration of FIG. 2, as described above, the groove width W1 of the wide portions 211, 221 and the groove width W2 of the narrow portions 212, 222 in each of the circumferential grooves 21, 22 (see FIG. 3) are constant.

[0122] On the other hand, in the configuration of FIG. 21, the groove widths W1 (see FIG. 3) of the wide portions 211 and 221 in the circumferential grooves 21 and 22 respectively increase and decrease periodically at each pitch. Also, at this time, it is preferable that the groove width W1 [mm] of the wide portions 211 and 221 is in the range of 0.025 ≦ W1 / SW ≦ 0.070 with respect to the total tire width SW [mm].

[0123] Also, in the configuration of FIG. 22, the groove widths W2 (see FIG. 3) of the narrow portions 212 and 222 in the circumferential grooves 21 and 22 respectively increase and decrease periodically at each pitch. Also, at this time, it is preferable that the groove width W2 [mm] of the narrow portions 212 and 222 is in the range of 0.001 ≦ W2 / SW ≦ 0.024 with respect to the total tire width SW [mm].

[0124] Also, in the configuration of FIG. 2, as described above, the first and second circumferential grooves 21 and 22 are arranged asymmetrically left and right about the tire equatorial plane CL. Specifically, they are at different distances G1W < G2W from the tire equatorial plane CL, and are arranged with a phase difference φ2 (see FIG. 3) of the wide portions 211 and 221 in the tire circumferential direction. Also, the lug grooves 311 and 312 in the inner region in the vehicle width direction and the lug grooves 321 in the outer region in the vehicle width direction also have mutually asymmetric structures.

[0125] On the other hand, in the configurations of FIGS. 23 and 24, the first and second circumferential grooves 21 and 22 are arranged symmetrically left and right about the tire equatorial plane CL. Specifically, they are at the same distance G1W = G2W from the tire equatorial plane CL, and are arranged with the phases of the wide portions 211 and 221 in the tire circumferential direction aligned (φ2 = 0 in FIG. 3). Also, the lug grooves 311 and 312 in the inner region in the vehicle width direction and the lug grooves 321 and 322 in the outer region in the vehicle width direction also have mutually symmetric structures.

[0126] [Effect] As described above, [1] the tire 1 includes a plurality of circumferential grooves 21, 22 and a plurality of land portions 31-33 partitioned by the plurality of circumferential grooves 21, 22 (see FIG. 2). The tire outer diameter OD [mm] (see FIG. 1) is in the range of 200≦OD≦660, and the tire total width SW [mm] is in the range of 100≦SW≦400. At least one of the plurality of circumferential grooves 21, 22 has a groove shape formed by alternately connecting wide portions 211; 221 and narrow portions 212; 222 (see FIG. 2). In addition, the groove width W1 [mm] of the wide portions 211, 221 is in the range of 0.025≦W1 / SW≦0.070 with respect to the total tire width SW [mm], and the groove width W2 [mm] of the narrow portions 212, 222 is in the range of 0.001≦W2 / SW≦0.024 with respect to the total tire width SW [mm].

[0127] In this configuration, the wide portions 211, 221 of the circumferential grooves 21, 22 ensure drainage in the tread center region, improving the wet performance of the tire, and the narrow portions 212, 222 ensure rigidity in the tread center region, improving the wear resistance of the tire. This has the advantage of achieving both wet performance and wear resistance of the tire. In particular, small-diameter tires with tire outer diameters OD and total tire widths SW in the above ranges are required to have high load capacity, so there is a problem that the wear resistance of the tire deteriorates due to an increase in tire ground pressure, and the wet performance of the tire deteriorates due to a decrease in tire ground contact area. In this respect, by providing such a small-diameter tire with the above configuration, there is an advantage that the wet performance and wear resistance of the tire can be significantly improved.

[0128] [2] In the tire 1 described in [1] above, the minimum value _min of the groove width W2 [mm] of the narrow portions 212, 222 is in the range of 0.10≦W2_min / W1_max≦0.50 relative to the maximum value W1_max [mm] of the wide portions 211, 221. The lower limit has the advantage of ensuring the wet performance of the tire, and the upper limit has the advantage of ensuring the wear resistance of the tire.

[0129] [3] In the tire 1 described in [1] or [2] above, the circumferential length L1 [mm] (see FIG. 3) of the wide portions 211, 221 is in the range of 0.025≦L1 / OD≦0.065 relative to the tire outer diameter OD [mm] (see FIG. 1), and the circumferential length L2 [mm] of the narrow portions 212, 222 is in the range of 0.015≦L2 / OD≦0.055 relative to the tire outer diameter OD [mm]. The lower limit of the circumferential length L1 of the wide portions 211, 221 and the upper limit of the circumferential length L2 of the narrow portions 212, 222 ensure the wet performance of the tire, and the upper limit of the circumferential length L1 of the wide portions 211, 221 and the lower limit of the circumferential length L2 of the narrow portions 212, 222 have the advantage of ensuring the wear resistance of the tire.

[0130] [4] In the tire 1 according to any one of the above items [1] to [3], the pitch length P2 (see FIG. 3) of the circumferential grooves 21, 22 consisting of the wide portions 211, 221 and the narrow portions 212, 222 is in the range of 0.20≦P2 / LA≦0.60 relative to the tire contact length LA [mm] (not shown). This has the advantage that the tire's wet performance and wear resistance can be efficiently achieved at the same time.

[0131] [5] In the tire 1 according to any one of [1] to [4] above, the plurality of circumferential grooves 21, 22 include a first circumferential groove 21 and a second circumferential groove 22 each having a wide portion 211, 221 and a narrow portion 212, 222 (see FIG. 2). The wide portion 211 of the first circumferential groove 21 and the wide portion 221 of the second circumferential groove 22 are arranged in a staggered manner in the tire circumferential direction. This has the advantage that the drainage performance of the tread central region is improved, the wet performance of the tire is improved, and the rigidity of the tread central region in the tire circumferential direction is uniformed, improving the wear resistance of the tire.

[0132] [6] In the tire 1 according to any one of the above items [1] to [5], the number G [of the circumferential grooves 21, 22 is in the range of 0.010≦G / SW≦0.025 with respect to the total tire width SW [mm]. This has the advantage that the tire has both good wet performance and good wear resistance.

[0133] [7] In the tire 1 described in any one of [1] to [6] above, the groove width W2' [mm] (not shown) of the narrow width portions 212, 222 when the tire is mounted on a specified rim, a specified internal pressure is applied, and a specified load is applied, and the groove width W2 [mm] of the narrow width portions 212, 222 when no load is applied (see FIG. 3) are in the range of -15≦|W2'-W2| / W2×100-RL≦+15 with respect to the load load rate RL [%] when the specified load is applied. This has the advantage that the rate of change of the groove width W2' of the narrow width portions 212, 222 is approximately proportional to the load load rate RL [%], effectively achieving both wet performance and wear resistance of the tire.

[0134] [8] In the tire 1, the tire 1 is described in any one of [1] to [7] above. Among the multiple circumferential grooves 21, 22, a center circumferential groove 21 is disposed in one region (inner region in the vehicle width direction in FIG. 2) that is closest to the tire equatorial plane CL and a shoulder circumferential groove 22 is disposed in the other region (outer region in the vehicle width direction in FIG. 2) and is the outermost in the tire width direction (see FIG. 2). The center circumferential groove 21 in one region and the shoulder circumferential groove 22 in the other region have a groove shape that alternately connects wide portions 211, 221 and narrow portions 212, 222. The distance G1W [mm] from the tire equatorial plane CL to the center circumferential groove 21 in one region is in the range of 0.20≦G1W / G2W≦0.85 with respect to the distance G2W [mm] from the tire equatorial plane CL to the shoulder circumferential groove 22 in the other region. This has the advantage that the wear resistance and drainage performance of the tire are improved, particularly when the tire 1 is mounted on a vehicle with the central circumferential groove 21 in one region having the distance G1W facing inward in the vehicle width direction.

[0135] [9] In the tire 1 according to any one of [1] to [8] above, the sum ΣSc [mm^2] of groove areas Sc1, Sc2 in the tire ground contact region of the multiple circumferential grooves is in the range of 0.01≦(ΣSc) / Sr≦0.15 with respect to the area Sr [mm^2] of the tire ground contact region. The lower limit has the advantage of ensuring drainage in the tread central region, and the upper limit has the advantage of ensuring rigidity in the tread central region.

[0136]

[10] In the tire 1 according to any one of the above items [1] to [9], the groove area ratio of the tire contact region is in the range of 1% to 16%. This has the advantage of ensuring the wet performance and wear resistance of the tire.

[0137]

[11] In the tire 1 according to any one of [1] to

[10] above, a pair of shoulder circumferential grooves 21, 22 at the outermost positions in the tire width direction among the multiple circumferential grooves 21, 22 are defined, and a pair of shoulder land portions 31, 32 defined by the pair of shoulder circumferential grooves 21, 22 are defined (see FIG. 2). Each of the pair of shoulder land portions 31, 32 includes lug grooves 311, 312, 321 that intersect with the tire ground contact edge T at one end and terminate inside the shoulder land portions 31, 32 at the other end. This improves drainage in the shoulder region of the tread, which is advantageous in improving wet performance of the tire.

[0138]

[12] In the tire 1 described in [1] above, the strength Tcs [N / 50mm] per 50 [mm] of the carcass ply constituting the carcass layer 13 is in the range of 17≦Tcs / OD≦120 relative to the tire outer diameter OD [mm]. This ensures the structural strength of the small-diameter tire, thereby ensuring an appropriate tire contact shape during tire rolling, and thus improving the wet performance and wear resistance of the tire. EXAMPLES

[0139] 25 and 26 are tables showing the results of performance tests of the tires according to the embodiments of the present invention.

[0140] In this performance test, multiple types of test tires were evaluated for (1) wear resistance and (2) wet performance. Two types of test tires were used as examples of small-diameter tires. Specifically, [A] a test tire with a tire size of 145 / 80R12 was mounted on a rim with a rim size of 12×4.00B, and an internal pressure of 80% of the JATMA-specified internal pressure and 80% of the JATMA-specified load were applied to the test tire. [B] a test tire with a tire size of 235 / 45R10 was mounted on a rim with a rim size of 10×8, and an internal pressure of 230 kPa and a load of 4.2 kN were applied. The test tires were mounted on all wheels of a four-wheel low-floor vehicle, which was the test vehicle.

[0141] (1) In the evaluation of wear resistance, a test vehicle runs 10,000 km on a test course on dry roads, and then the amount of wear on the test tires is measured and evaluated. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the better.

[0142] (2) In the evaluation of wet performance, the test vehicle runs on an asphalt road sprayed with water 1mm deep at a speed of 40km / h. Then, the test driver performs a sensory evaluation of the steering performance when changing lanes and cornering, and the stability when going straight. This evaluation is performed using an index evaluation with the comparative example as the standard (100), and the higher the value, the better.

[0143] 1 and 2, and includes a pair of circumferential grooves 21, 22 and a plurality of lug grooves 311, 312, 321. On the other hand, the test tire of the comparative example has the configuration of Example 1, but the pair of circumferential grooves 21, 22 have a straight shape with a constant groove width.

[0144] As the test results show, the test tires of the examples have both good wet performance and good wear resistance. [Explanation of symbols]

[0145] 1 tire; 11 bead core; 12 bead filler; 13 carcass layer; 14 belt layer; 141, 142 cross belt; 143 belt cover; 144 belt edge cover; 15 tread rubber; 151 cap tread; 152 under tread; 16 sidewall rubber; 17 rim cushion rubber; 18 inner liner; 21, 22 circumferential groove; 211, 221 wide portion; 212, 222 narrow portion; 31-33 land portion; 311, 312 lug groove; 321 lug groove

Claims

1. A tire having a plurality of circumferential grooves and a plurality of land portions defined by the plurality of circumferential grooves, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, At least one of the plurality of circumferential grooves has a groove shape formed by alternately connecting wide portions and narrow portions, The groove width W1 [mm] of the wide portion is in the range of 0.025≦W1 / SW≦0.070 with respect to the total tire width SW [mm], and A tire characterized in that a groove width W2 [mm] of the narrow width portion is in the range of 0.001≦W2 / SW≦0.024 with respect to a total tire width SW [mm].

2. 2. The tire according to claim 1, wherein a minimum value W2_min of the groove width W2 [mm] of the narrow width portion is in a range of 0.10≦W2_min / W1_max≦0.50 with respect to a maximum value W1_max of the groove width W1 [mm] of the wide width portion.

3. 2. The tire according to claim 1, wherein a circumferential length L1 [mm] of the wide portion is in a range of 0.025≦L1 / OD≦0.065 relative to the tire outer diameter OD [mm], and a circumferential length L2 [mm] of the narrow portion is in a range of 0.015≦L2 / OD≦0.055 relative to the tire outer diameter OD [mm].

4. 2. The tire according to claim 1, wherein a pitch length P2 of the circumferential groove consisting of the wide portion and the narrow portion is in a range of 0.20≦P2 / LA≦0.60 with respect to a tire contact length LA [mm].

5. 2. The tire according to claim 1, wherein the plurality of circumferential grooves include a first circumferential groove and a second circumferential groove each having the wide portion and the narrow portion, and the wide portion of the first circumferential groove and the wide portion of the second circumferential groove are arranged in a staggered manner in the tire circumferential direction.

6. The tire according to claim 1 , wherein the number G of the plurality of circumferential grooves is in a range of 0.010≦G / SW≦0.025 with respect to a total tire width SW [mm].

7. 2. The tire according to claim 1, wherein the groove width W2' [mm] of the narrow portion when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and subjected to a specified load, and the groove width W2 [mm] of the narrow portion when in an unloaded state, are in a range of -15≦|W2'-W2| / W2×100-RL≦+15 relative to the load load rate RL [%] when the specified load is applied.

8. 2. The tire according to claim 1, wherein among the plurality of circumferential grooves, a center circumferential groove is disposed in one region having the tire equatorial plane as a boundary, and a shoulder circumferential groove is disposed in the other region and is on the outermost side in the tire width direction, the center circumferential groove in the one region and the shoulder circumferential groove in the other region have a groove shape formed by alternately connecting the wide portion and the narrow portion, and a distance G1W [mm] from the tire equatorial plane to the center circumferential groove in the one region is in a range of 0.20≦G1W / G2W≦0.85 with respect to a distance G2W [mm] from the tire equatorial plane to the shoulder circumferential groove in the other region.

9. The tire according to claim 1, wherein a sum of groove areas ΣSc [mm^2] of the plurality of circumferential grooves in the tire ground contact region is in a range of 0.01≦(ΣSc) / Sr≦0.15 with respect to an area Sr [mm^2] of the tire ground contact region.

10. 2. The tire according to claim 1, wherein a groove area ratio of the tire contact region is in the range of 1% to 16%.

11. 2. The tire according to claim 1, further comprising: a pair of shoulder circumferential grooves that are located at the outermost sides in the tire width direction among the plurality of circumferential grooves; a pair of shoulder land portions that are partitioned by the pair of shoulder circumferential grooves; and each of the pair of shoulder land portions has a lug groove that intersects with a tire ground contact edge at one end and terminates inside the shoulder land portion at the other end.

12. 2. The tire according to claim 1, wherein a strength Tcs [N / 50 mm] per 50 mm width of the carcass ply constituting the carcass layer is in a range of 17≦Tcs / OD≦120 with respect to an outer diameter OD [mm] of the tire.

Images