tire

Abstract

To provide a tire that can improve resistance to irregular tread wear.SOLUTION: Provided is a tire where in the case where a circumferential main groove 30 positioned at the outermost part in a tire width direction out of a plurality of circumferential main grooves 30 is the outermost main groove 32, and a radius of a profile P on a tire meridian section of a portion positioned between the outermost main grooves 32 on a tread surface 3 of a tread part 2 is a center radius CR, the center radius CR in a state where a pneumatic tire 1 is installed to a specified rim and inflated to a specified internal pressure is R600 mm or more. Regarding the outermost main groove 32, a difference D=Ga-Gb between a groove depth Ga from a position of an inner opening end 32a being an inner opening end in the tire width direction to a groove bottom 32c of the outermost main groove 32 and a groove depth Gb from a position of an outer opening end 32b being an outer opening end in the tire width direction to the groove bottom 32c is within a range of 0.3 mm≤D≤1.5 mm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] When the tread surface of a tire wears, uneven wear may occur depending on the shape of the land portion, etc., so some conventional tires have been designed to prevent uneven wear. For example, in a pneumatic tire described in Patent Document 1, the entire first land portion formed outermost in the tire width direction is spaced inward from an imaginary extension line of an outer contour line that follows the tread surface of a second land portion adjacent to the first land portion in the tire width direction, the tread surface of the center rib follows the outer contour line, and the tire width direction distances H1, H2 between the imaginary extension line and the inner end and outer end of the first land portion in the tire width direction, respectively, are such that H1 > H2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4303343 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in recent years, a decrease in wear life due to uneven wear has been raised as an issue for tires, and even higher uneven wear resistance is required.

[0005] The present invention has been made in view of the above, and has an object to provide a tire that can improve uneven wear resistance. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the objects, the tire according to the present invention has a tread portion including a plurality of circumferential main grooves extending in the tire circumferential direction and a plurality of land portions defined by the plurality of circumferential main grooves, wherein the circumferential main groove that is located outermost in the tire width direction among the plurality of circumferential main grooves is defined as an outermost main groove, and the radius of a profile in a tire meridian cross section of a portion of the tread surface of the tread portion located between the outermost main grooves is defined as a center radius, the center radius when the tire is mounted on a specified rim and inflated to a specified internal pressure is R600 mm or more, and the outermost main groove has a groove depth Ga from the position of the inner opening edge in the tire width direction to the groove bottom of the outermost main groove and a groove depth Gb from the position of the outer opening edge in the tire width direction to the groove bottom, where D=Ga-Gb, is within a range of 0.3 mm≦D≦1.5 mm. [Effects of the Invention]

[0007] The tire according to the present invention has an effect of improving uneven wear resistance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a meridian cross-sectional view showing a main part of a pneumatic tire according to an embodiment. [Figure 2] FIG. 2 is a view taken along the line AA in FIG. [Figure 3] FIG. 3 is a detailed view of the outermost main groove shown in FIG. [Figure 4] FIG. 4 is a detailed view of one side of the tread portion shown in FIG. 1 in the tire width direction. [Figure 5] FIG. 5 is a schematic plan view of the lug groove in which the sipe shown in FIG. 2 is arranged. [Figure 6] 6 is a BB cross-sectional view taken along the extending direction of the lug grooves shown in FIG. [Figure 7] FIG. 7 is a schematic diagram showing the ground contact shape of the pneumatic tire according to the embodiment. [Figure 8]FIG. 8 is a plan view of a tread portion 2 of a modified example of the pneumatic tire according to the embodiment, in which no sipes are arranged. [Figure 9] FIG. 9 is a table showing the results of a performance evaluation test of pneumatic tires. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of a tire according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0010] [Embodiment] In the following description, a pneumatic tire 1 will be used as an example of a tire according to the present invention. The pneumatic tire 1, which is an example of a tire, can be filled with air, an inert gas such as nitrogen, or other gases.

[0011] In the following description, the tire radial direction refers to the direction perpendicular to the rotation axis (not shown) of the pneumatic tire 1, the tire radial inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radial outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotation axis as the central axis. The tire width direction refers to the direction parallel to the rotation axis, the tire width inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides in position in the tire width direction with the tire width centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire width is the width in the tire width direction between the outermost portions in the tire width direction, i.e., the distance between the portions farthest from the tire equatorial plane CL in the tire width direction. The tire equator line refers to a line that is on the tire equatorial plane CL and extends along the tire circumferential direction of the pneumatic tire 1.

[0012] FIG. 1 is a meridian cross-sectional view showing a main portion of a pneumatic tire 1 according to an embodiment. In this embodiment, a heavy-duty pneumatic radial tire mounted on heavy-duty vehicles such as trucks and buses will be described as an example. When viewed in a meridian cross-section, the pneumatic tire 1 according to this embodiment has a tread portion 2 disposed on the outermost side in the tire radial direction. The surface of the tread portion 2, i.e., the portion that comes into contact with the road surface when a vehicle (not shown) equipped with the pneumatic tire 1 is traveling, is formed as a tread surface 3. A plurality of circumferential main grooves 30 extending in the tire circumferential direction are formed in the tread surface 3, and the plurality of circumferential main grooves 30 are arranged side by side in the tire width direction. In this embodiment, four circumferential main grooves 30 are arranged side by side in the tire width direction. Furthermore, a plurality of land portions 20 are defined on the tread surface 3 by the circumferential main grooves 30 arranged side by side in the tire width direction.

[0013] The circumferential main groove 30 referred to here is a longitudinal groove extending in the tire circumferential direction, and has a wear indicator (slip sign) therein that indicates the end of wear.

[0014] Both ends of the tread portion 2 in the tire width direction are formed as shoulder portions 4, and the ends of the tread surface 3 in the tire width direction at the shoulder portions 4 are shoulder points 4a. The shoulder points 4a are the intersections of the surfaces of the buttress portions located on both sides of the tread portion 2 in the tire width direction and the tread surface 3. Sidewall portions 5 are arranged from the shoulder portions 4 to a predetermined position on the inner side in the tire radial direction. In other words, the sidewall portions 5 are provided at two locations on both sides of the pneumatic tire 1 in the tire width direction.

[0015] Furthermore, bead portions 10 are disposed on the tire radially inner side of each sidewall portion 5, and like the sidewall portions 5, the bead portions 10 are provided at two locations on both sides of the tire equatorial plane CL in the tire width direction. That is, a pair of bead portions 10 are disposed on both sides of the tire equatorial plane CL in the tire width direction. A bead core 11 is disposed in each of the pair of bead portions 10, and a bead filler 15 is disposed on the tire radially outer side of each bead core 11. The bead core 11 is formed by winding a bead wire, which is a steel wire, into a ring shape. The bead filler 15 is a rubber material disposed in a space formed by folding back the tire width direction end of the carcass 6 (described later) outward in the tire width direction at the position of the bead core 11.

[0016] A belt layer 7 is disposed on the tire radially inner side of the tread portion 2. The belt layer 7 has a multi-layer structure in which, for example, four belt layers 7a, 7b, 7c, and 7d are laminated, and is formed by coating a plurality of belt cords made of steel or organic fiber material such as polyester, rayon, or nylon with coating rubber and rolling them. The belts 7a, 7b, 7c, and 7d have different belt angles, which are defined as the inclination angle of the belt cords in the tire width direction with respect to the tire circumferential direction, and are laminated so that the inclination directions of the belt cords cross each other, forming a so-called cross-ply structure.

[0017] A carcass 6 containing radial ply cords is continuously provided on the tire radially inward side of the belt layer 7 and on the tire equatorial plane CL side of the sidewall portion 5. The carcass 6 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 bead cores 11 arranged on both sides in the tire width direction to form the tire framework. More specifically, the carcass 6 is arranged from one bead portion 10 to the other of a pair of bead portions 10 located on both sides in the tire width direction, and is wound back at the bead portions 10 along the bead cores 11 to the outside in the tire width direction so as to enclose the bead cores 11 and bead fillers 15. The carcass ply of the carcass 6 arranged in this manner is formed by coating multiple carcass cords made of steel or organic fiber material such as polyester, rayon, or nylon with coating rubber and rolling them.

[0018] An inner liner 8 is disposed along the carcass 6 on the inner side of the carcass 6 or on the inner side of the carcass 6 in the pneumatic tire 1 .

[0019] 2 is a view taken along the arrow AA in FIG. 1. The four circumferential main grooves 30 formed on the tread surface 3 include two center main grooves 31, which are circumferential main grooves 30 arranged on both sides of the tire equatorial plane CL in the tire width direction, and two outermost main grooves 32, which are circumferential main grooves 30 located outermost in the tire width direction among the four circumferential main grooves 30. That is, the two outermost main grooves 32 are arranged on both sides of the center main groove 31 in the tire width direction, and the two outermost main grooves 32 are also arranged on both sides of the tire equatorial plane CL in the tire width direction with respect to the tire equatorial plane CL. Furthermore, both the center main groove 31 and the outermost main grooves 32 extend in the tire circumferential direction while repeatedly bending in the tire width direction. That is, the center main groove 31 and the outermost main grooves 32 are formed in a zigzag shape by extending in the tire circumferential direction while oscillating in the tire width direction.

[0020] These circumferential main grooves 30 have a groove width in the range of 10 mm to 15 mm, and a groove depth in the range of 12 mm to 20 mm.

[0021] Furthermore, of the multiple land portions 20, the land portion 20 located between two center main grooves 31 is a center land portion 21, the land portion 20 located between adjacent center main grooves 31 and outermost main grooves 32 in the tire width direction is a middle land portion 22, and the land portion 20 located outside the outermost main groove 32 in the tire width direction is a shoulder land portion 23.

[0022] Specifically, the center land portion 21 is defined on both sides in the tire width direction by two center main grooves 31. The middle land portion 22 is defined on the inside in the tire width direction by the center main groove 31 and on the outside in the tire width direction by the outermost main groove 32. The shoulder land portion 23 is defined on the inside in the tire width direction by the outermost main groove 32 and on the outside in the tire width direction by the end of the tread portion 2 in the tire width direction; that is, the shoulder point 4a is located at the end of the shoulder land portion 23 on the outside in the tire width direction.

[0023] In addition to the circumferential main grooves 30, a plurality of lug grooves 40 extending in the tire width direction are formed on the tread surface 3. In this embodiment, the lug grooves 40 include a center lug groove 41 that is a lug groove 40 arranged between two center main grooves 31, a middle lug groove 42 that is a lug groove 40 arranged between the center main groove 31 and the outermost main groove 32 that are adjacent in the tire width direction, and shoulder lug grooves 43 and second shoulder lug grooves 44 that are arranged on the outer side of the outermost main groove 32 in the tire width direction.

[0024] Of these, the center lug groove 41 extends in the tire width direction between the two center main grooves 31, with both ends opening into the center main groove 31. The middle lug groove 42 extends in the tire width direction between the adjacent center main groove 31 and outermost main groove 32, with its inner end in the tire width direction opening into the center main groove 31 and its outer end in the tire width direction opening into the outermost main groove 32. Both the center lug groove 41 and the outermost main groove 32 are formed in a zigzag shape that extends in the tire width direction and bends repeatedly in the tire circumferential direction.

[0025] The shoulder lug grooves 43 are positioned outside the outermost main groove 32 in the tire width direction, extend in the tire width direction, and are so-called semi-closed lug grooves with one end opening into the outermost main groove 32 and the other end terminating within the shoulder land portion 23. The second shoulder lug grooves 44 are positioned outside the outermost main groove 32 in the tire width direction, and are so-called closed lug grooves with both ends in the extension direction of the lug grooves 40 terminating within the shoulder land portion 23.

[0026] These lug grooves 40 have a groove width in the range of 0.5 mm to 5 mm, and a groove depth in the range of 2 mm to 10 mm.

[0027] A plurality of center lug grooves 41 and a plurality of middle lug grooves 42, both ends of which open into the circumferential main groove 30, are arranged side by side in the tire circumferential direction. Therefore, the center land portion 21 and the middle land portion 22 are defined on both sides in the tire circumferential direction by the lug grooves 40, forming so-called block-shaped land portions 20. In other words, the center land portion 21 is defined on both sides in the tire circumferential direction by the center lug grooves 41 adjacent in the tire circumferential direction, and the middle land portion 22 is defined on both sides in the tire circumferential direction by the middle lug grooves 42 adjacent in the tire circumferential direction, forming a block-shaped land portion 20.

[0028] Furthermore, a plurality of sipes 50 are formed on the tread surface 3. In this embodiment, the sipes 50 include a center sipe 51 and a middle sipe 52.

[0029] The sipes 50 referred to here are narrow grooves formed on the tread surface 3 or groove bottoms, and when the pneumatic tire 1 is mounted on a specified rim and under a specified internal pressure condition and no load is applied, the wall surfaces constituting the narrow grooves do not come into contact with each other. However, when a load is applied vertically on a flat plate and the narrow grooves are located in the land portions 20 that form the contact patch on the flat plate, the wall surfaces constituting the narrow grooves, or at least parts of the portions provided on the wall surfaces, come into contact with each other due to deformation of the land portions 20. In this embodiment, the sipes 50 have a groove width of 1.0 mm or less.

[0030] Specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. 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.

[0031] The center sipes 51 are so-called groove bottom sipes that are disposed at the groove bottom of the center lug grooves 41 located between the two center main grooves 31. The center sipes 51 are disposed in every other center lug groove 41 among the center lug grooves 41 that are arranged side by side in the tire circumferential direction. In other words, the center lug grooves 41 that have center sipes 51 disposed at the groove bottom and the center lug grooves 41 that do not have center sipes 51 disposed are disposed alternately in the tire circumferential direction.

[0032] The middle sipes 52 are so-called groove bottom sipes that are disposed at the groove bottoms of the middle lug grooves 42 located between adjacent center main groove 31 and outermost main groove 32. Of the multiple middle lug grooves 42 that are arranged side by side in the tire circumferential direction, the middle sipes 52 are disposed in every other middle lug groove 42. In other words, the middle lug grooves 42 that have middle sipes 52 disposed at the groove bottoms and middle lug grooves 42 that do not have middle sipes 52 disposed are disposed alternately in the tire circumferential direction.

[0033] Since there are no lug grooves 40 or sipes 50 that penetrate the shoulder land portion 23 in the tire width direction on the outer side of the outermost main groove 32, the shoulder land portion 23 is a so-called rib-shaped land portion 20 that is formed continuously in the tire circumferential direction.

[0034] The multiple land portions 20 formed on the tread surface 3 by the circumferential main grooves 30 and lug grooves 40 in this manner constitute a land portion row 25. That is, the multiple center land portions 21 located between two center main grooves 31 and aligned in the tire circumferential direction constitute a center land portion row 26, which is a land portion row 25 in which multiple block-shaped center land portions 21 are aligned in the tire circumferential direction. Also, the multiple middle land portions 22 located between adjacent center main grooves 31 and outermost main grooves 32 and aligned in the tire circumferential direction constitute a middle land portion row 27, which is a land portion row 25 in which multiple block-shaped middle land portions 22 are aligned in the tire circumferential direction. Also, the shoulder land portions 23 located on the outer side of the outermost main groove 32 in the tire width direction constitute a shoulder land portion row 28, which is a land portion row 25 in which rib-shaped shoulder land portions 23 extend in the tire circumferential direction.

[0035] Of these land rows 25, the center land row 26 and the middle land row 27 are land rows 25 that are partitioned on both sides in the tire width direction by circumferential main grooves 30. Therefore, a plurality of land rows 25 that are partitioned on both sides in the tire width direction by circumferential main grooves 30 are arranged on the inside of the outermost main grooves 32 of the tread surface 3 in the tire width direction.

[0036] In the pneumatic tire 1 having the tread portion 2 configured as above, the relationship between the developed tread width TW and the total tire width SW is within the range of 0.55≦TW / SW≦0.95 when the pneumatic tire 1 is mounted on a standard rim and inflated to a standard internal pressure. The relationship between the developed tread width TW and the total tire width SW is preferably within the range of 0.70≦TW / SW≦0.95.

[0037] The tread developed width TW here is the dimension obtained by expanding the tread surface 3 between the ground contact edges T on both sides in the tire width direction. The ground contact edges T are defined as the maximum width position in the tire width direction at the contact surface between the pneumatic tire 1 and a flat plate when the pneumatic tire 1 is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate and subjected to a load corresponding to a specified load. In this embodiment, the ground contact edges T are located at substantially the same position as the shoulder points 4a.

[0038] The total tire width SW is measured as the linear distance between the sidewalls 5 (including all parts such as patterns and letters on the side of the tire) when the pneumatic tire 1 is mounted on a specified rim, pressurized to the specified internal pressure, and in an unloaded state. 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.

[0039] Furthermore, the pneumatic tire 1 according to this embodiment has a center radius CR, which is the radius of the profile P in the tire meridian cross section of the tread surface 3 of the tread portion 2, located between the outermost main grooves 32, and is R600 mm or more. In this case, the center radius CR is the radius of the profile P in the tire meridian cross section of the tread surface 3 located between the outermost main grooves 32 in the tire width direction when the pneumatic tire 1 is mounted on a standard rim and inflated to a standard internal pressure. In other words, the center radius CR here does not include the radius of the profile P of the tread surface 3 located on the outer side of the outermost main grooves 32 in the tire width direction. In other words, the profile P in the portion of the tread surface 3 located between the outermost main grooves 32 is arc-shaped in the tire meridian cross section, and the center radius CR is the radius of curvature of the arc that is the shape of the profile P. The center radius CR is preferably R700 mm or more.

[0040] FIG. 3 is a detailed view of the outermost main groove 32 shown in FIG. 1 . Of the outermost main grooves 32 arranged on both sides of the pneumatic tire 1 in the tire width direction, FIG. 3 is a detailed view of the outermost main groove 32 located on the right side of the page in FIG. 1 . The circumferential main groove 30 of the pneumatic tire 1 according to this embodiment has a narrow width portion 30c where the groove width is narrowed in a portion closer to the groove bottom. That is, the circumferential main groove 30 has a platform portion 30b formed in a portion of the groove wall 30a closer to the groove bottom, where the groove wall 30a is substantially parallel to the tread surface 3, and the portion closer to the groove bottom than the platform portion 30b is the narrow width portion 30c. Therefore, in the circumferential main groove 30, the groove wall of the narrow width portion 30c located closer to the groove bottom than the platform portion 30b is smaller in width than the portion of the circumferential main groove 30 located closer to the tread surface 3 than the platform portion 30b.

[0041] The land portions 20 located on both sides of the outermost main groove 32 in the tire width direction have tread surfaces 3 at different positions in the tire radial direction. Specifically, the tread surface 3 of the shoulder land portion 23 located on the outer side of the outermost main groove 32 in the tire width direction is located more inward in the tire radial direction than the tread surface 3 of the middle land portion 22 located on the inner side of the outermost main groove 32 in the tire width direction. In other words, the tread surface 3 of the shoulder land portion 23 is located more inward in the tire radial direction than the profile P of the tread surface 3 of the land portion 20 located on the inner side of the outermost main groove 32 in the tire width direction.

[0042] For this reason, the outer opening end 32b of the outermost main groove 32, which is the opening end on the outer side in the tire width direction, is located radially inward of the inner opening end 32a, which is the opening end on the inner side in the tire width direction of the outermost main groove 32. As a result, the groove depth Gb of the outermost main groove 32 measured from the outer opening end 32b to the groove bottom 32c is smaller than the groove depth Ga of the outermost main groove 32 measured from the inner opening end 32a to the groove bottom 32c. Specifically, the difference D = Ga - Gb between the groove depth Ga from the inner opening end 32a to the groove bottom 32c of the outermost main groove 32 and the groove depth Gb from the outer opening end 32b to the groove bottom 32c of the outermost main groove 32 is within the range of 0.3 mm≦D≦1.5 mm.

[0043] In this case, the groove depth Ga is the distance between an imaginary line V that extends parallel to the profile P of the tread surface 3 and is tangent to the groove bottom 32c of the outermost main groove 32, and the inner opening end 32a of the outermost main groove 32. Similarly, the groove depth Gb is the distance between the outer opening end 32b of the outermost main groove 32 and the imaginary line V. The difference D between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b, measured in this manner, is preferably within the range of 0.5 mm≦D≦1.5 mm.

[0044] Fig. 4 is a detailed view of one side of the tread portion 2 shown in Fig. 1 in the tire width direction. Fig. 4 is a detailed view of a portion of the tread portion 2 located to the right of the tire equatorial plane CL on the page of Fig. 1. The size of the tread surface 3 in the tire radial direction decreases from the vicinity of the tire equatorial plane CL, which is located in the center in the tire width direction, toward both ends in the tire width direction. Therefore, shoulder points 4a, which are located at the ends of the tread surface 3 in the tire width direction, are located radially inward of the position near the tire equatorial plane CL, which is the portion of the tread surface 3 where the size in the tire radial direction is greatest.

[0045] Specifically, the tread portion 2 has a shoulder drop amount S, which is the distance in the tire radial direction between a maximum diameter portion M, which is the portion located at the outermost side in the tire radial direction in a profile P of the tread surface 3 when the pneumatic tire 1 is mounted on a standard rim and inflated to a standard internal pressure, and a shoulder point 4a, within the range of 4 mm≦S≦15 mm. In this case, the maximum diameter portion M of the profile P of the tread surface 3 is substantially the portion of the profile P where the tire equatorial plane CL and the profile P intersect. The shoulder drop amount S of the tread portion 2 determined in this manner is preferably within the range of 4 mm≦S≦10 mm.

[0046] Fig. 5 is a schematic plan view of a lug groove 40 in which the sipe 50 shown in Fig. 2 is arranged. Fig. 6 is a BB cross-sectional view taken along the extension direction of the lug groove 40 shown in Fig. 5. The center lug groove 41 and the middle lug groove 42, which are lug grooves 40 arranged between the outermost main grooves 32 in the tire width direction, each have a groove depth Gg that is 70% or less of the groove depth G (see Fig. 4) of the circumferential main groove 30. In this case, when the circumferential main groove 30 is the outermost main groove 32, the groove depth G of the circumferential main groove 30 is the groove depth Ga (see Fig. 3) at the position of the inner opening end 32a of the outermost main groove 32.

[0047] Furthermore, the sipes 50 disposed at the groove bottoms 40a of these center lug grooves 41 and middle lug grooves 42, i.e., the sipes 50 disposed between the outermost main grooves 32 in the tire width direction, also have a depth Gp that is 70% or less of the groove depth G of the circumferential main grooves 30. In this case, the depth Gp of the sipes 50 is the depth from the tread surface 3.

[0048] The sipes 50 may be arranged so as to open directly to the tread surface 3. In addition, the groove depth Gg of the lug grooves 40 arranged between the outermost main grooves 32 in the tire width direction and the depth Gp of the sipes 50 are preferably 50% or less of the groove depth G of the circumferential main grooves 30.

[0049] When mounting the pneumatic tire 1 according to this embodiment on a vehicle, the pneumatic tire 1 is mounted on a rim wheel, filled with air, and mounted on the vehicle in an inflated state. When a vehicle mounted with the pneumatic tire 1 runs, the pneumatic tire 1 rotates while the lower portion of the tread surface 3 of the tread portion 2 comes into contact with the road surface. When a vehicle mounted with the pneumatic tire 1 runs on a dry road surface, the vehicle runs by transmitting driving force and braking force to the road surface and generating turning force mainly due to friction between the tread surface 3 and the road surface.

[0050] Furthermore, when traveling on a wet road surface, water between the tread surface 3 and the road surface enters grooves such as the circumferential main grooves 30 and lug grooves 40, and these grooves drain the water between the tread surface 3 and the road surface while traveling. This makes it easier for the tread surface 3 to make contact with the road surface, and the frictional force between the tread surface 3 and the road surface enables the vehicle to travel.

[0051] When a vehicle equipped with the pneumatic tire 1 travels, the tread surface 3 contacts the road surface as described above, and the tread portion 2 gradually wears from the tread surface 3 side of the land portion 20. If the degree of wear differs among the multiple land rows 25 of the tread portion 2, uneven wear may easily occur.

[0052] In contrast, in the pneumatic tire 1 of this embodiment, the center radius CR is R600 mm or more, and the difference D = Ga - Gb between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b is within the range of 0.3 mm ≦ D ≦ 1.5 mm, making it less likely for uneven wear to occur.

[0053] 7 is a schematic diagram showing a contact shape 60 of a pneumatic tire 1 according to this embodiment. A plurality of land rows 25 are arranged side by side in the tire width direction on the tread surface 3 of the pneumatic tire 1, so that when the tread surface 3 comes into contact with the ground, each of the land rows 25 comes into contact with the ground. Furthermore, in the pneumatic tire 1 according to this embodiment, the plurality of land rows 25 arranged on the inner sides of the two outermost main grooves 32 have approximately the same contact length when in contact with the ground.

[0054] Specifically, when the pneumatic tire 1 is mounted on a specified rim, inflated to a specified internal pressure, and the tread surface 3 is brought into contact with the ground under a standard maximum load, the contact lengths L of the land rows 25 arranged on the inside of the two outermost main grooves 32 are within a range of 90% to 110% of each other between adjacent land rows 25. In other words, when the tread surface 3 of the pneumatic tire 1 is brought into contact with the ground under the above conditions, the contact length L1 of the center land row 26 is within a range of 90% to 110% of the contact length L2 of the middle land row 27 adjacent to the center land row 26.

[0055] For this reason, when the tread surface 3 comes into contact with the ground, the contact shape 60 of the contact surface is formed by the plurality of land rows 25 arranged on the inside of the two outermost main grooves 32 in the tire width direction, and is a substantially rectangular shape. In other words, the contact shape 60 formed by the plurality of land rows 25 arranged on the inside of the two outermost main grooves 32 has a substantially rectangular shape because the positions of the front and rear ends of the contact shape 60, i.e., the positions of the leading side and trailing side in the tire rotation direction, are close to each other for the land rows 25.

[0056] When the tread surface 3 is brought into contact with the ground under the above conditions, it is preferable that the contact length L of the land rows 25 arranged on the inside of the two outermost main grooves 32 be within the range of 95% or more and 105% or less between adjacent land rows 25.

[0057] The pneumatic tire 1 according to this embodiment has a center radius CR of R600 mm or more when inflated to a specified internal pressure, so that the outer diameters of the tread surface 3 of the land portions 20 located between the two outermost main grooves 32 can be made similar to each other. In other words, because the center radius CR is R600 mm or more, of the land portions 20 located between the two outermost main grooves 32, the outer diameter of the tread surface 3 of the land portion 20 located closer to the tire equatorial plane CL and the outer diameter of the tread surface 3 of the land portion 20 located closer to the outermost main groove 32 can be made similar to each other.

[0058] This allows the contact lengths L of the land rows 25 located between the two outermost main grooves 32 to be close to each other, and the contact pressure of the land portions 20 located between the two outermost main grooves 32 to be made closer to uniform. Therefore, the wear rates of the land portions 20 can be made similar, thereby suppressing uneven wear.

[0059] Furthermore, the outermost main groove 32 has a difference D between the groove depth Ga at the inner opening end 32a and the groove depth Gb at the outer opening end 32b within a range of 0.3 mm≦D≦1.5 mm, so that when the tread surface 3 comes into contact with the ground, the shoulder land portion 23, which is the land portion 20 located on the outer side of the outermost main groove 32 in the tire width direction, can make appropriate contact with the ground. In other words, if the difference D between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b is D<0.3 mm, the difference D between the groove depths Ga and Gb is too small, making it easier for the shoulder land portion 23 to make contact with the ground. In this case, the ground pressure of the land portion 20 located between the two outermost main grooves 32 and closer to the outermost main groove 32 becomes smaller, making it difficult to achieve uniform ground pressure for the land portions 20 located between the two outermost main grooves 32, and therefore making it difficult to suppress uneven wear of these land portions 20.

[0060] Furthermore, if the difference D between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b is D>1.5 mm, the difference D between the groove depths Ga and Gb is too large, making it difficult for the shoulder land portion 23 to contact the ground. In this case, the ground contact pressure of the land portion 20 located between the two outermost main grooves 32 that is closer to the outermost main groove 32 becomes large, making it difficult to make the ground contact pressure of the land portion 20 located between the two outermost main grooves 32 approach an equal ground contact pressure, and making it difficult to suppress uneven wear of these land portions 20.

[0061] In contrast, when the difference D between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b is within the range of 0.3 mm≦D≦1.5 mm, the shoulder land portion 23 can be brought into contact with the ground at an appropriate level. This allows the ground pressure of the land portion 20 located between the two outermost main grooves 32, which is closer to the outermost main groove 32, to be adjusted to an appropriate level, thereby making the ground pressure of the land portion 20 located between the two outermost main grooves 32 closer to the outermost main groove 32 closer to the outermost main groove 32 closer to the outermost main groove 32. Therefore, the wear rates of the multiple land portions 20 located between the two outermost main grooves 32 can be made approximately the same, suppressing uneven wear. As a result, uneven wear resistance can be improved.

[0062] Furthermore, when the pneumatic tire 1 is inflated to a specified internal pressure, the shoulder drop S, which is the radial distance between the maximum diameter portion M of the profile P of the tread surface 3 and the shoulder point 4a, is within the range of 4 mm≦S≦15 mm, allowing the shoulder land portions 23 to adequately contact the ground when the tread surface 3 contacts the ground. In other words, if the shoulder drop S is less than 4 mm, the shoulder drop S is too small, making it easier for the shoulder land portions 23 located on the outer side of the outermost main groove 32 in the tire width direction to contact the ground, and there is a risk that the contact length of the shoulder land portions 23 when the tread surface 3 contacts the ground may be too long. In this case, the shoulder land portions 23 are more susceptible to wear, which may increase the risk of so-called shoulder wear, which is uneven wear in which the portions of the tread surface 3 closer to the shoulder portions 4 wear out earlier than the portions closer to the tire equatorial plane CL.

[0063] Furthermore, if the shoulder drop amount S is S>15 mm, the shoulder drop amount S is too large, which may make it difficult for the shoulder land portions 23 to come into contact with the ground, resulting in an excessively small contact area of ​​the shoulder land portions 23. In this case, when the tread surface 3 comes into contact with the ground, the land portions 20 located between the two outermost main grooves 32 are more susceptible to wear than the shoulder land portions 23, which may result in uneven wear in which the portion of the tread surface 3 closer to the tire equatorial plane CL wears out earlier than the portion closer to the shoulder portions 4, i.e., so-called center wear.

[0064] In contrast, when the shoulder drop amount S is within the range of 4 mm≦S≦15 mm, the shoulder land portions 23 can be brought into contact with the ground appropriately when the tread surface 3 comes into contact with the ground. This makes it more difficult for the shoulder land portions 23 to come into contact with the ground than the land portions 20 located between the two outermost main grooves 32, while also making the contact area of ​​the shoulder land portions 23 appropriately large. This allows the wear rates of the land portions 20 located between the two outermost main grooves 32 and the shoulder land portions 23 to be approximately the same, thereby suppressing uneven wear. As a result, uneven wear resistance can be improved.

[0065] Furthermore, since the relationship between the tread developed width TW and the tire total width SW of the pneumatic tire 1 is within the range of 0.55≦TW / SW≦0.95, uneven wear of the land portions 20 located between the two outermost main grooves 32 can be suppressed. In other words, if the relationship between the tread developed width TW and the tire total width SW is TW / SW<0.55, the tread developed width TW is too small, and even if there is a difference D between the groove depth Ga at the inner opening end 32a of the outermost main groove 32 and the groove depth Gb at the outer opening end 32b, the shoulder land portions 23 may easily come into contact with the ground. In this case, the ground contact pressure of the land portions 20 located between the two outermost main grooves 32 and closer to the outermost main groove 32 becomes smaller, making it difficult to make the ground contact pressure of the land portions 20 located between the two outermost main grooves 32 closer to the outermost main groove 32 uniform, and thus making it difficult to suppress uneven wear of these land portions 20.

[0066] Furthermore, if the relationship between the tread developed width TW and the tire total width SW is TW / SW>0.95, the tread developed width TW is too large, which may make it easier for the land portions 20 located between the two outermost main grooves 32 to come into contact with the ground, while making it relatively more difficult for the shoulder land portions 23 to come into contact with the ground. In this case, the ground contact pressure of the land portions 20 located between the two outermost main grooves 32, which are closer to the outermost main groove 32, becomes greater, making it difficult to make the ground contact pressure of the land portions 20 located between the two outermost main grooves 32 approach an equal ground contact pressure, and making it difficult to suppress uneven wear of these land portions 20.

[0067] In contrast, because the relationship between the tread developed width TW and the tire total width SW is within the range of 0.55≦TW / SW≦0.95, the shoulder land portions 23 can be brought into appropriate contact with the ground. This allows the ground pressure of the land portions 20 located between the two outermost main grooves 32, which are closer to the outermost main grooves 32, to be adjusted to an appropriate level, thereby making it possible to make the wear rates of the land portions 20 located between the two outermost main grooves 32 approximately the same, thereby suppressing uneven wear. As a result, uneven wear resistance can be improved.

[0068] Furthermore, in the tread portion 2, the lug grooves 40 and sipes 50 arranged between the outermost main grooves 32 in the tire width direction have a depth of 70% or less of the groove depth G of the circumferential main grooves 30, which prevents the rigidity of the land portions 20 arranged between the outermost main grooves 32 from becoming too low. This prevents the land portions 20 located between the two outermost main grooves 32 from easily bending, which can lead to uneven wear. As a result, uneven wear resistance can be improved.

[0069] Furthermore, when the pneumatic tire 1 is brought into contact with the ground under the standard maximum load, the contact lengths L of the land rows 25 are within a range of 90% to 110% of each other between adjacent land rows 25, so the wear rates of the land rows 25 arranged on the inside of the outermost main grooves 32 can be made to be approximately the same. As a result, uneven wear resistance can be improved.

[0070] [Variations] In the above-described embodiment, a center sipe 51 is arranged in the center land row 26 and a middle sipe 52 is arranged in the middle land row 27, but any or all of these sipes 50 may not be arranged.

[0071] 8 is a plan view of a tread portion 2 of a modified example of the pneumatic tire 1 according to the embodiment, in which sipes 50 are not provided. For example, the center lug grooves 41 arranged in the center land row 26 and the middle lug grooves 42 arranged in the middle land row 27 do not need to have center sipes 51 or middle sipes 52. The center lug grooves 41 and middle lug grooves 42 arranged between two outermost main grooves 32 do not need to have sipes, as long as the lug groove groove depth Gg is 70% or less of the groove depth G of the circumferential main grooves 30.

[0072] Also, the shoulder land row 28 may not be provided with the second shoulder lug groove 44, and only the shoulder lug groove 43 may be provided. Alternatively, the shoulder land row 28 may be provided with a sipe 50 that opens at one end to either the outermost main groove 32 or the shoulder point 4a and terminates at the other end within the shoulder land portion 23. It is preferable that a lug groove 40 or a sipe 50 that opens at one end to either the shoulder point 4a or the outermost main groove 32 and terminates at the other end within the shoulder land portion 23 is provided on the outer side of the outermost main groove 32 in the tire width direction.

[0073] The lug grooves 40 and sipes 50 arranged in the shoulder land row 28 do not open at both ends to the shoulder point 4a and the outermost main groove 32, and at least one end terminates within the shoulder land portion 23, thereby preventing the rigidity of the shoulder land portion 23 from becoming too low. This prevents the shoulder land portion 23 from wearing out earlier than the center land portion 21 and middle land portion 22, thereby preventing uneven shoulder wear. As a result, uneven wear resistance can be improved.

[0074] In the above-described embodiment, four circumferential main grooves 30 are arranged, but the number of circumferential main grooves 30 may be other than four. The number of circumferential main grooves 30 may be, for example, three, five or more. In the embodiment, the circumferential main grooves 30 have the terraced portions 30b and the narrow portions 30c, but the circumferential main grooves 30 do not have to have the terraced portions 30b or the narrow portions 30c.

[0075] In the present embodiment, as described above, a pneumatic tire 1 has been described as an example of a tire. The pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, or other gases. However, the tread pattern configuration of the pneumatic tire 1 described in the present embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires.

[0076] [Example] 9 is a table showing the results of a performance evaluation test of the pneumatic tire 1. Hereinafter, a description will be given of a performance evaluation test conducted on the conventional pneumatic tire 1 and the pneumatic tire 1 according to the present invention with respect to the above-mentioned pneumatic tire 1. The performance evaluation test was conducted to test uneven wear resistance.

[0077] The performance evaluation test was carried out under the condition that a pneumatic tire 1 having a tire nominal size of 11R22.5 was mounted on a rim wheel having a rim size of 22.5 x 7.50, and the air pressure was adjusted to the specified air pressure.

[0078] The uneven wear resistance was evaluated by mounting the test tire on a test vehicle and conducting a road test. Among the groove depths of the multiple circumferential main grooves 30, the groove depth of the circumferential main groove 30 with the deepest remaining groove depth was compared with the groove depth of the circumferential main groove 30 with the smallest groove depth. The uneven wear resistance was evaluated by expressing the reciprocal of the difference in the groove depth of the circumferential main grooves 30 as an index, with the conventional example described below being set at 100. The larger this index value, the less uneven wear there was in the land portion 20, and the better the uneven wear resistance. Furthermore, since a larger index value indicates less uneven wear in the land portion 20, the larger the index value, the longer the estimated wear life.

[0079] The performance evaluation test was conducted on 15 types of pneumatic tires, including conventional pneumatic tires and Examples 1 to 14, which are pneumatic tires 1 according to the present invention. Of these, the conventional pneumatic tires had a groove depth difference D of the outermost main grooves 32 that was not within the range of 0.3 mm≦D≦1.5 mm.

[0080] In contrast, Examples 1 to 14, which are examples of the pneumatic tire 1 according to the present invention, all have a center radius CR of 600 mm or more and a groove depth difference D of the outermost main grooves 32 within the range of 0.3 mm≦D≦1.5 mm. Furthermore, the pneumatic tires 1 according to Examples 1 to 14 are different from one another in the shoulder drop amount S, the ratio of the developed tread width TW to the total tire width SW (TW / SW), the groove depth Gg of the lug grooves 40 relative to the groove depth G of the circumferential main grooves 30, the opening of the shoulder lug grooves 43, and the ratio of the contact length L2 of the middle land row 27 to the contact length L1 of the center land row 26.

[0081] Performance evaluation tests were conducted using these pneumatic tires 1, and the results showed that the pneumatic tires 1 according to Examples 1 to 14 all had improved uneven wear resistance compared to the conventional tire, as shown in Fig. 9. In other words, the pneumatic tires 1 according to Examples 1 to 14 had improved uneven wear resistance.

[0082] The present disclosure encompasses the following inventions. Invention[1] In the tread area, a plurality of circumferential main grooves extending in the tire circumferential direction; a plurality of land portions defined by the plurality of circumferential main grooves; A tire comprising: Among the plurality of circumferential main grooves, the circumferential main groove located outermost in the tire width direction is defined as an outermost main groove, When the radius of a profile in a tire meridian cross section of a portion located between the outermost main grooves on the tread surface of the tread portion is defined as a center radius, The center radius when the tire is mounted on a specified rim and inflated to a specified internal pressure is R600 mm or more, The outermost main groove has a groove depth Ga from the position of the inner opening edge in the tire width direction to the groove bottom of the outermost main groove, and a groove depth Gb from the position of the outer opening edge in the tire width direction to the groove bottom, where D=Ga-Gb, which is within a range of 0.3 mm≦D≦1.5 mm. Invention[2] The tire according to invention [1], wherein the shoulder drop S, which is the distance in the tire radial direction between the part of the tread surface located at the outermost position in the tire radial direction in the profile when the tire is mounted on a specified rim and inflated to a specified internal pressure, is within the range of 4 mm≦S≦15 mm. Invention[3] A tire according to invention [1] or invention [2], wherein the relationship between the tread width TW and the total tire width SW when the tire is mounted on a specified rim and inflated to a specified internal pressure is within the range of 0.55≦TW / SW≦0.95. Invention[4] A tire according to any one of inventions [1] to [3], wherein lug grooves or sipes whose depth is 70% or less of the groove depth of the circumferential main grooves are arranged between the outermost main grooves in the tire width direction in the tread portion. Invention[5] A tire according to any one of inventions [1] to [4], wherein a lug groove or a sipe is arranged on the outside of the outermost main groove in the tire width direction, the lug groove or the sipe having one end opening to either the end of the tread surface in the tire width direction or the outermost main groove, and the other end terminating within the land portion. Invention[6] A plurality of land rows are arranged on the inner sides of the outermost main grooves in the tire width direction, and both sides in the tire width direction are partitioned by the circumferential main grooves, A tire according to any one of inventions [1] to [5], wherein when the tire is mounted on a specified rim, inflated to a specified internal pressure, and brought into contact with the ground under a standard maximum load, the contact lengths of the land rows are within a range of 90% to 110% of each other between adjacent land rows. [Explanation of symbols]

[0083] 1 pneumatic tire 2 Tread section 3 Tread surface 4 Shoulder section 4a Shoulder Point 5 Sidewall 6. Carcass 7 Belt Layer 8 Inner liner 10 Bead section 20 Land 21 Center Land Section 22 Middle Land Division 23 Shoulder land area 25 Rikubu row 26 Center Land Section 27 Middle Land Section 28 Shoulder Land Column 30 Circumferential main groove 31 Center main groove 32 Outermost main groove 32a Inner open end 32b Outer open end 32c groove bottom 40 lug groove 41 Center lug groove 42 Middle lug groove 43 Shoulder lug groove 44 Second shoulder lug groove 50 sipes 51 Center sipe 52 Middle sipe 60 Grounding shape

Claims

1. In the tread area, a plurality of circumferential main grooves extending in the tire circumferential direction; a plurality of land portions defined by the plurality of circumferential main grooves; A tire comprising: Among the plurality of circumferential main grooves, the circumferential main groove located outermost in the tire width direction is defined as an outermost main groove, When the radius of a profile in a tire meridian cross section of a portion located between the outermost main grooves on the tread surface of the tread portion is defined as a center radius, The center radius when the tire is mounted on a specified rim and inflated to a specified internal pressure is R600 mm or more, The outermost main groove has a groove depth Ga from the position of the inner opening end in the tire width direction to the groove bottom of the outermost main groove, and a groove depth Gb from the position of the outer opening end in the tire width direction to the groove bottom, where D = Ga - Gb, which is within a range of 0.3 mm ≦ D ≦ 1.5 mm.

2. 2. The tire according to claim 1, wherein a shoulder drop S, which is the distance in the tire radial direction between the outermost part of the tread surface in the profile in the tire radial direction and the end of the tread surface in the tire width direction when the tire is mounted on a specified rim and inflated to a specified internal pressure, is within a range of 4 mm≦S≦15 mm.

3. 2. The tire according to claim 1, wherein the relationship between the tread developed width TW and the total tire width SW when the tire is mounted on a specified rim and inflated to a specified internal pressure is within the range of 0.55≦TW / SW≦0.

95.

4. The tire according to claim 1, wherein the tread portion has lug grooves or sipes arranged between the outermost main grooves in the tire width direction, the lug grooves or sipes having a depth that is 70% or less of the groove depth of the circumferential main grooves.

5. 2. The tire according to claim 1, wherein a lug groove or a sipe is arranged on the outer side of the outermost main groove in the tire width direction, the lug groove or the sipe having one end opening to either the end of the tread surface in the tire width direction or the outermost main groove, and the other end terminating within the land portion.

6. A plurality of land rows are arranged on the inner sides of the outermost main grooves in the tire width direction, and both sides in the tire width direction are partitioned by the circumferential main grooves, 2. The tire according to claim 1, wherein when the tire is mounted on a specified rim, inflated to a specified internal pressure, and brought into contact with the ground under a standard maximum load, the contact lengths of the land rows of adjacent land rows are within a range of 90% to 110% of each other.

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