tire

Abstract

To improve low rolling resistance and wet performance. [Solution] The tread surface 15A has a plurality of circumferential main grooves 21, a center portion 31 between each of the outermost circumferential main grooves 21 in the tire width direction, circumferential narrow grooves 22 in the center portion 31 that are narrower in width than the circumferential main grooves 21, a center land portion 31A, 31B in the center portion 31 that is divided by the circumferential main grooves 21 and the circumferential narrow grooves 22, and both ends of the center land portion 31A, 31B are open to the circumferential main grooves 21 and the circumferential narrow grooves 22. The tire includes multiple narrow grooves 40 arranged in the circumferential direction, with their openings facing each other across the circumferential groove 22, and arranged so that the angle with respect to the center line of the circumferential groove 22 changes for each of them, and the groove width is narrower than that of the circumferential main groove 21, and a chamfered portion 50 that is positioned in the center land portion 31A, 31B, on the low-angle side formed by each of the facing narrow grooves 40 in the circumferential direction, extending from the groove opening of the circumferential groove 21 to the groove opening of the narrow groove 40 in the circumferential direction.

Description

Technical Field

[0001] This invention relates to a tire.

Background Art

[0002] For example, in Patent Document 1, in a pneumatic heavy-duty tire having a pair of circumferential main grooves extending along the circumferential direction of the tire disposed on the tread surface with the tire equatorial plane interposed therebetween, and the tread surface is divided into a central region and both side regions, at least one circumferential narrow groove extending along the circumferential direction of the tire is disposed in the central region to partition and form at least two or more central rib-shaped land portions. When the tire contacts the ground, the openings of the circumferential narrow grooves are closed, and a configuration is shown in which the central rib-shaped land portions adjacent to each other across the circumferential narrow grooves contact and support each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a method for improving rolling resistance, a center-biased pattern in which the main groove in the center portion is made into a narrow groove to suppress deformation of the center block with high contact pressure is used. However, in this center-biased pattern, there is a concern that the narrow groove closes during grounding in the grounding area of the center portion, and sufficient groove volume cannot be ensured, resulting in deterioration of wet performance.

[0005] An object of this invention is to provide a tire capable of improving low rolling resistance performance and wet performance.

Means for Solving the Problems

[0006] To achieve the above objective, a tire according to one aspect of the present invention includes, on the tread surface, at least two circumferential main grooves extending along the tire circumferential direction, a center portion partitioned between each of the outermost circumferential main grooves in the tire width direction, circumferential narrow grooves in the center portion that extend along the tire circumferential direction and are arranged to have a groove width narrower than the circumferential main grooves, a center land portion partitioned by the circumferential main grooves and the circumferential narrow grooves in the center portion, a plurality of widthwise narrow grooves in the center land portion that extend along the tire width direction and have both ends opening into the circumferential main grooves and circumferential narrow grooves, and are arranged in the tire circumferential direction with respect to the center line of the circumferential narrow grooves changing for each of the openings facing each other across the circumferential narrow grooves, and having a groove width narrower than the circumferential main grooves, and a chamfer portion in the center land portion that is arranged from at least one groove opening of the circumferential narrow groove to the groove opening of the widthwise narrow groove on the low-angle side formed by each of the widthwise narrow grooves whose openings face each other across the circumferential narrow grooves. [Effects of the Invention]

[0007] This invention makes it possible to improve low rolling resistance performance and wet performance. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a meridional cross-sectional view of a pneumatic tire according to an embodiment. [Figure 2] Figure 2 is a plan view of the tread surface of a pneumatic tire according to an embodiment. [Figure 3] Figure 3 is an enlarged plan view of the tread surface of a pneumatic tire according to an embodiment. [Figure 4] Figure 4 is a schematic plan view of the tread surface of a pneumatic tire according to an embodiment. [Figure 5] Figure 5 is a schematic plan view of the tread surface of a pneumatic tire according to an embodiment. [Figure 6] Figure 6 is a schematic cross-sectional view of the tread surface of a pneumatic tire according to an embodiment. [Figure 7]Figure 7 is a schematic cross-sectional view of the tread surface of a pneumatic tire according to an embodiment. [Figure 8] Figure 8 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 9] Figure 9 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited by these embodiments. Furthermore, the components of these embodiments include those that are substituted and obvious for substitution while maintaining the identity of the invention. In addition, the multiple modifications described in these embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[0010] In the following description, the tire radial direction refers to the direction perpendicular to the tire rotation axis (not shown), which is the rotation axis of the pneumatic tire 1 of the embodiment. The inner side of the tire radial direction refers to the side toward the tire rotation axis in the tire radial direction, and the outer side of the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side of the tire width direction refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the outer side of the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the tire rotation axis and passing through the center of the tire width of the pneumatic tire 1. The position of the tire equatorial plane CL in the tire width direction coincides with the tire width direction center line, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line on the tire equatorial plane CL that runs along the tire circumferential direction of the pneumatic tire 1. Furthermore, a meridional cross-section of a tire (meridian section) refers to the cross-section obtained when the tire is cut along a plane containing the tire's axis of rotation.

[0011] Figure 1 shows a meridional cross-section of the pneumatic tire 1 of the embodiment, illustrating a cross-section of one side of the tire rotation axis in the tire radial direction. In this embodiment, as an example, a heavy-duty pneumatic radial tire mounted on heavy-duty vehicles such as trucks and buses will be described. The pneumatic tire 1 of this embodiment is particularly suitable for use on the drive axle of a heavy-duty vehicle.

[0012] The pneumatic tire 1 of this embodiment has an annular structure centered on the tire rotation axis, and as shown in Figure 1, comprises a pair of bead cores 11, a pair of bead fillers 12, a carcass layer 13, a belt layer 14, tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers 17.

[0013] Each pair of bead cores 11 is formed by winding one or more bead wires made of steel in a ring-like and multi-layered manner, and is embedded in the bead portion to form the core of the bead portion on both sides in the width direction of the tire.

[0014] The pair of bead fillers 12 are positioned on the outer circumference of the tire in the radial direction of the pair of bead cores 11 to reinforce the bead portion.

[0015] 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. The carcass layer 13 is toroidally stretched between the two bead cores 11 to form the framework of the tire. The ends of the carcass layer 13 are also wrapped around the bead cores 11 and bead filler 12 and secured outward in the tire width direction. The carcass ply of the carcass layer 13 is constructed by covering multiple carcass cords made of steel with a coating rubber and then rolling it, and has a cord angle (defined as the inclination angle of the carcass cord in the longitudinal direction relative to the tire circumferential direction) of 80[°] to 90[°] in absolute value for radial tires, and 30[°] to 45[°] for bias tires.

[0016] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144 and is disposed around the outer circumference of the carcass layer 13. These belt plies 141 to 144 include a high-angle belt 141, a pair of intersecting belts 142 and 143, and a belt cover 144. The high-angle belt 141 is formed by covering a plurality of steel belt cords with a coat rubber and subjecting them to rolling, and has, for example, a cord angle (defined as the inclination angle of the longitudinal direction of the belt cord with respect to the tire circumferential direction) of 45° or more and 70° or less in absolute value. The pair of intersecting belts 142 and 143 are formed by covering a plurality of steel belt cords with a coat rubber and subjecting them to rolling, and have, for example, a cord angle of 10° or more and 55° or less in absolute value. Also, the pair of intersecting belts 142 and 143 have cord angles of opposite signs and are laminated with the longitudinal directions of the belt cords intersecting each other (having a so-called cross-ply structure). The belt cover 144 is formed by covering a plurality of belt cover cords made of steel or an organic fiber material with a coat rubber and subjecting them to rolling, and has, for example, a cord angle of 10° or more and 55° or less in absolute value.

[0017] The tread rubber 15 is disposed on the outer circumference in the tire radial direction of the carcass layer 13 and the belt layer 14 and constitutes the tread portion of the pneumatic tire 1. The tread rubber 15 forms a tread surface (tread tread) 15A on the outer peripheral surface that contacts the road surface during running in the tread portion.

[0018] A pair of sidewall rubbers 16 are respectively disposed on the outer sides in the tire width direction of the carcass layer 13 and constitute the sidewall portions on both sides in the tire width direction.

[0019] A pair of rim cushion rubbers 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the winding portions of each bead core 11 and the carcass layer 13 and constitute the rim fitting surfaces of the bead portions.

[0020] As shown in Figure 2, the pneumatic tire 1 of the embodiment has a tread pattern on the tread surface 15A. Here, each dimension of the tread pattern is measured with the tire mounted without a rim, with the width between the pair of bead portions set to the specified rim width.

[0021] A specified rim refers to a "standard rim" as defined by JATMA, a "design rim" as defined by TRA, or a "measuring rim" as defined by ETRTO. Furthermore, specified internal pressure refers to the "maximum air pressure" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "INFLATION PRESSURES" as defined by ETRTO. Finally, specified load refers to the "maximum load capacity" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "LOAD CAPACITY" as defined by ETRTO.

[0022] The groove width is measured as the maximum distance between opposing groove walls at the groove opening on the tread surface, with the tire mounted without a rim and the width between the pair of bead sections set to the specified rim width. In configurations where the groove opening has a notch or chamfer, the groove width is measured using the intersection of the extension line of the tread surface and the extension line of the groove wall as the endpoint in a cross section parallel to the tire width direction and tire diameter direction.

[0023] Groove depth is measured as the maximum distance from the tread surface to the bottom of the groove when the tire is mounted without a rim and the width between the pair of bead sections is set to the specified rim width. In configurations where the groove bottom has partial irregularities, these are excluded from the measurement.

[0024] The pneumatic tire 1 has a circumferential main groove 21, a circumferential narrow groove 22, a widthwise narrow groove 40, a chamfered portion 50, a rounded chamfered portion 60, and shallow grooves 71, 72 on its tread surface 15A.

[0025] The circumferential main grooves 21 extend along the circumferential direction of the tire and have an annular structure that is continuously provided around the entire circumference of the tire. At least two circumferential main grooves 21 are provided side by side in the tire width direction, with the tire equatorial plane CL in between. The circumferential main grooves 21 may be formed in a zigzag shape that extends along the circumferential direction of the tire and meanders in the tire width direction, as shown in Figure 2. The circumferential main grooves 21 have a groove width at the opening to the tread surface 15A (the narrowest width in the zigzag shape) of 10.0 [mm] or more and 18.0 [mm] or less, and a groove depth from the tread surface 15A to the bottom of the groove of 10.0 [mm] or more and 26.0 [mm] or less. The circumferential main grooves 21 are defined as grooves that have a requirement to display a treadwear indicator as specified by JATMA at the bottom of the groove.

[0026] The pneumatic tire 1 has a tread surface 15A that is divided into multiple sections in the tire width direction, separated by circumferential main grooves 21. The pneumatic tire 1 of this embodiment has a center section 31 divided between the two outermost circumferential main grooves 21 in the tire circumferential direction, and shoulder sections 32 that are each divided on the outer side of each circumferential main groove 21 in the tire width direction up to the contact edge T. The center section 31 is arranged to include the tire equatorial plane CL. The shoulder sections 32 are each arranged at the outermost edges of the tread surface 15A in the tire width direction.

[0027] Here, the contact end T is defined as the position of the maximum width in the tire width direction at the contact surface between the pneumatic tire 1 and the flat plate when the pneumatic tire 1 is mounted on a specified rim, a specified internal pressure is applied, and the tire is placed perpendicular to the flat plate and a load corresponding to a specified load is applied.

[0028] The circumferential groove 22 extends along the circumferential direction of the tire in the center portion 31 and has an annular structure that is continuously provided around the entire circumference of the tire. At least one circumferential groove 22 is provided. In the embodiment, two circumferential grooves 22 are provided side by side in the tire width direction. The circumferential groove 22 is formed in a linear shape along the circumferential direction of the tire. The circumferential groove 22 has a groove width W1 (dimension between groove openings 20a on the tread surface 15A: see Figures 3 and 6) of 1.0 [mm] to 3.0 [mm] and a groove depth H1 (dimension from the tread surface 15A to the groove bottom 20b: see Figure 6) of 8.0 [mm] to 26.0 [mm]. The circumferential groove 22 is formed with a groove width W1 narrower than that of the circumferential main groove 21.

[0029] The pneumatic tire 1 has a center portion 31 which is divided into multiple center land portions 31A and 31B arranged in the tire width direction, separated by circumferential narrow grooves 22. The pneumatic tire 1 of this embodiment has two circumferential narrow grooves 22, a single row of center land portions 31A divided between each circumferential narrow groove 22, and two rows of center land portions 31B divided on the outer side of each circumferential narrow groove 22 in the tire width direction. In the pneumatic tire 1 of this embodiment, the center land portion 31A is located in the center in the tire width direction, including the tire equatorial plane CL. In addition, in the pneumatic tire 1 of this embodiment, each center land portion 31B is divided between adjacent circumferential narrow grooves 22 and circumferential main grooves 21 in the tire width direction.

[0030] The widthwise narrow grooves 40 extend along the tire width direction in each center land area 31A, 31B, with both ends opening into the circumferential main groove 21 and circumferential narrow groove 22, and are arranged in a row in the circumferential direction of the tire. The widthwise narrow grooves 40 are formed in a straight or curved shape. As shown in Figure 7, the widthwise narrow grooves 40 include a first widthwise narrow groove 41 with a relatively wide groove width W2 and a relatively deep groove depth H2, and a second widthwise narrow groove 42 with a relatively narrow groove width W3 and a relatively shallow groove depth H3. These first widthwise narrow grooves 41 and second widthwise narrow grooves 42 are arranged in a mixed manner in the circumferential direction of the tire in each center land area 31A, 31B. In the pneumatic tire 1 of this embodiment, the first widthwise narrow grooves 41 and second widthwise narrow grooves 42 are arranged alternately in the circumferential direction of the tire in a 2-in-1 arrangement in each center land area 31A, 31B. The first widthwise narrow groove 41 has a main body portion 41A having a groove width W2, and a sipe 41B extending inward in the tire radial direction from the groove bottom 40b of the main body portion 41A. The groove width W2 of the first widthwise narrow groove 41 (dimension between groove openings 40a of the main body portion 41A on the tread surface 15A: see Figure 7) is 1.5 [mm] or more and 3.0 [mm] or less (preferably 2.0 [mm]). The width of the sipe 41B of the first widthwise narrow groove 41 is less than 1.0 [mm]. The groove depth H2 of the first widthwise narrow groove 41 (dimension including the main body portion 41A and sipe 41B from the tread surface 15A: see Figure 7) is 10.0 [mm] or more and 20.0 [mm] or less (preferably 14.5 [mm]). The first widthwise narrow groove 41 has a ratio of 40% to 60% (preferably 50%) of the main body 41A to the sipe 41B at a groove depth H2. The second widthwise narrow groove 42 has a groove width W3 (dimension between groove openings 40a on the tread surface 15A: see Figure 7) of 1.0 mm to 2.0 mm (preferably 1.2 mm). The second widthwise narrow groove 42 has a groove depth H3 (dimension from the tread surface 15A to the groove bottom 40b: see Figure 7) of 0.5 mm to 3.0 mm (preferably 1.5 mm). The widthwise narrow grooves 40 (first widthwise narrow groove 41, second widthwise narrow groove 42) are formed with narrower groove widths W2 and W3 compared to the circumferential main groove 21.

[0031] As shown in Figures 3 to 5, the widthwise narrow grooves 40 are arranged so that their openings 40o face each other with respect to the circumferential narrow grooves 22. In the pneumatic tire 1 of this embodiment, the openings 40o of the first widthwise narrow grooves 41 face each other, and the openings 40o of the second widthwise narrow grooves 42 face each other. When viewed in a plan view in the radial direction of the tire, the widthwise narrow grooves 40 whose openings 40o face each other are arranged with a change in angle with respect to the center line C of the circumferential narrow groove 22 (a straight line passing through the center of the groove width W1: see Figure 3), and are not parallel to each other. The angle of the widthwise narrow groove 40 with respect to the center line C is measured by a straight line connecting each position at 5% of the length extending from the opening 40o. Because the widthwise narrow grooves 40 whose openings 40o face each other are not parallel to each other, the angle they make with each other forms a high-angle side L and a low-angle side S within a range of 360°. The angle between the opposing narrow grooves 40 in the width direction of the opening 40o is less than 180° on the lower angle side S, and preferably between 100° and 160°.

[0032] As shown in Figure 6, the chamfered portion 50 is formed to cut out the groove opening 20a of the circumferential narrow groove 22. As shown in Figures 3 to 5, the chamfered portion 50 is positioned on the low-angle side S of the opposing widthwise narrow grooves 40, from the groove opening 20a of the circumferential narrow groove 22 to the groove opening 40a of the widthwise narrow groove 40. The chamfered portion 50 may be positioned over the opposing widthwise narrow grooves 40, but preferably over one of the opposing widthwise narrow grooves 40. In the pneumatic tire 1 of the embodiment, the chamfered portion 50 is positioned at the groove opening 20a on the circumferential main groove 21 side of each circumferential narrow groove 22 on the outermost side in the tire width direction. The chamfered portion 50 satisfies the relationship 0.5 ≤ W0 / W1 ≤ 2.5 for the maximum width W0 of the circumferential narrow groove 22 relative to the groove width W1, and the relationship 0.01 ≤ H0 / H1 ≤ 0.15 for the maximum depth H0 of the circumferential narrow groove 22 relative to the groove depth H1. The maximum depth H0 of the chamfered portion 50 is approximately 1.0 [mm].

[0033] As shown in Figure 3, the chamfered portion 50 has a maximum width W0 and maximum depth H0 in the portion of the chamfered portion 50 that is adjacent to the groove opening 40a of one of the widthwise narrow grooves 40 facing each other, and is formed to become narrower in width and shallower in depth as it moves away from the widthwise narrow groove 40. The chamfered portion 50 is positioned along the groove opening 20a of the circumferential narrow groove 22 between adjacent widthwise narrow grooves 40 in the tire width direction, and extends over one adjacent widthwise narrow groove 40 but not to the other adjacent widthwise narrow groove 40. The chamfered portion 50 is positioned along the groove opening 20a of the circumferential narrow groove 22 in a range of 70% to 100% of one pitch P (see Figure 2) between adjacent widthwise narrow grooves 40 in the tire width direction. In addition, as shown in Figure 3, the chamfered portion 50 has a plurality of shallow narrow grooves (also called microgrooves) 50a arranged on its surface. The shallow grooves 50a are, for example, grooves with a depth of 0.3 mm and a width of 0.6 mm, and are arranged in a row along the extending direction of the circumferential grooves 22 (tire circumferential direction), with their length decreasing as they move away from the widthwise grooves 40.

[0034] As shown in Figures 2 and 3, the R-chamfered portion 60 is positioned so as to curve and recess from the groove opening 20a of the circumferential groove 22 to the groove opening 40a of the widthwise groove 40 on the high-angle side L of the opposing widthwise narrow grooves 40 with the opening 40o facing each other. The R-chamfered portion 60 may be positioned over both of the opposing widthwise narrow grooves 40 with the opening 40o facing each other, but preferably it is positioned over one of the opposing widthwise narrow grooves 40 with the opening 40o facing each other. In the pneumatic tire 1 of the embodiment, if the chamfered portion 50 is positioned over one of the widthwise narrow grooves 40, the R-chamfered portion 60 is positioned over the other widthwise narrow groove 40. The R-chamfered portion 60 is formed to be shallower in width and depth than the chamfered portion 50. The radius of curvature of the R-chamfered portion 60 is R2 [mm] or more and R20 [mm] or less (preferably R7 [mm]).

[0035] The shallow grooves 71 and 72 are located on the tread surface 15A of the shoulder portion 32. The shallow groove 71 extends along the tire width direction, with one end opening into the outermost circumferential main groove 21 in the tire width direction and the other end opening at the contact end T. Multiple shallow grooves 71 are arranged in a row in the circumferential direction of the tire. The shallow grooves 71 are positioned so that their openings face the opening 40o of the width direction narrow groove 40 (first width direction narrow groove 41 in this embodiment) with respect to the circumferential main groove 21. The shallow grooves 71 are formed in a straight or curved shape. The shallow grooves 71 have the same groove width and groove depth as the second width direction narrow groove 42. The shallow grooves 71 are formed with a narrower groove width and shallower groove depth than the circumferential main groove 21.

[0036] The shallow grooves 72 are positioned between the shallow grooves 71. The shallow grooves 72 are formed as recesses that are recessed from the tread surface 15A. In the pneumatic tire 1 of this embodiment, the shallow grooves 72 are formed as triangular recesses that are recessed from the tread surface 15A. The shallow grooves 72 have a similar depth to the shallow grooves 71. The shallow grooves 71 are formed to be shallower in depth than the circumferential main grooves 21. Multiple shallow fine grooves (also called microgrooves) 72a are arranged on the bottom surface of the shallow grooves 72. The shallow fine grooves 72a have a depth of, for example, 0.3 [mm] and are arranged in a row along the circumferential direction of the tire.

[0037] The pneumatic tire 1 of the above-described embodiment is characterized by having at least two circumferential main grooves 21 extending along the tire circumferential direction on the tread surface 15A, a center portion 31 partitioned between each of the outermost circumferential main grooves 21 in the tire width direction, circumferential narrow grooves 22 in the center portion 31 that are arranged extending along the tire circumferential direction and have a groove width narrower than the circumferential main grooves 21, center land portions 31A, 31B partitioned by the circumferential main grooves 21 and the circumferential narrow grooves 22 in the center portion 31A, 31B that extend along the tire width direction The tire includes multiple widthwise narrow grooves 40 arranged in the circumferential direction of the tire, with both ends opening into the circumferential main groove 21 or the circumferential narrow groove 22, and the angle with respect to the center line C of the circumferential narrow groove 22 changes for each of the openings 40o facing each other across the circumferential narrow groove 22, and widthwise narrow grooves 40 that are narrower in width than the circumferential main groove 21, and a chamfered portion 50 that is positioned in the center land portion 31A, 31B, on the low-angle side S formed by each widthwise narrow groove 40 whose openings 40o face each other across the circumferential narrow groove 22, extending from at least one groove opening 20a of the circumferential narrow groove 22 to the groove opening 40a of the widthwise narrow groove 40.

[0038] With this pneumatic tire 1, by arranging circumferential grooves 22 in the center portion 31, the circumferential grooves 22 close when in contact with the ground, suppressing deformation of the center portion 31 and improving low rolling resistance performance. Moreover, with this pneumatic tire 1, by having widthwise grooves 40 and chamfered portions 50, the groove openings of the circumferential grooves 22 are secured, ensuring drainage, and the edge effect of the widthwise grooves 40 improves wet performance. Furthermore, with this pneumatic tire 1, by having chamfered portions 50 on the low-angle side S formed by each widthwise groove 40 facing each other at the opening 40o, chipping of the tread surface 15A on the low-angle side S is suppressed.

[0039] Furthermore, in the pneumatic tire 1 of this embodiment, the widthwise narrow grooves 40 include a first widthwise narrow groove 41 with a relatively wide groove width W2 and a second widthwise narrow groove 42 with a relatively narrow groove width W3, and in the center land portion 31A, 31B, the first widthwise narrow groove 41 and the second widthwise narrow groove 42 are arranged in a mixed manner in the tire circumferential direction.

[0040] According to this pneumatic tire 1, by arranging the first widthwise narrow groove 41 and the second widthwise narrow groove 42 in a mixed (preferably alternating) manner in the circumferential direction of the tire, the rigidity of the center land portion 31A, 31B is maintained, improving low rolling resistance performance and wet performance.

[0041] Furthermore, in the pneumatic tire 1 of this embodiment, the widthwise narrow groove 40 includes a first widthwise narrow groove 41 with a relatively wide groove width W2 and a relatively deep groove depth H2, and having a sipe 41B at the groove bottom 40b, and a second widthwise narrow groove 42 with a relatively narrow groove width W3 and a relatively shallow groove depth H3, and in the center land portion 31A, 31B, the first widthwise narrow groove 41 and the second widthwise narrow groove 42 are arranged in a mixed manner in the tire circumferential direction.

[0042] With this pneumatic tire 1, by arranging the first widthwise narrow grooves 41 and the second widthwise narrow grooves 42 in a mixed (preferably alternating) manner in the circumferential direction of the tire, the rigidity of the center land portion 31A, 31B is maintained, improving low rolling resistance performance and wet performance. Moreover, with this pneumatic tire 1, the sipes 41B of the first widthwise narrow grooves 41 close at the bottom of the groove 40b when in contact with the ground, thus ensuring better drainage and improving wet performance.

[0043] Furthermore, in the pneumatic tire 1 of this embodiment, the chamfered portion 50 is formed so that its width W0 gradually narrows and its depth H0 becomes shallower as it moves away from the widthwise narrow groove 40 along the circumferential narrow groove 22.

[0044] With this pneumatic tire 1, when in contact with the ground, a large gap and contact area can be secured on the tread surface on the side of the narrow groove 40 in the width direction, and wet performance can be improved in a balanced way with low rolling resistance performance.

[0045] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, the dimension Wa of the center portion 31 in the tire width direction, the dimension Wb of the center land portions 31A and 31B in the tire width direction, and the number A of the circumferential narrow grooves 22 satisfy the relationship 0.7 ≤ Wb(A+1) / Wa < 1.0. Note that in the pneumatic tire 1 of the embodiment, the circumferential main groove 21 has a zigzag shape, and in this case, the chamfered portion 50 at the widest part in the tire width direction is ignored when taking the dimension Wb in the tire width direction.

[0046] In this pneumatic tire 1, the width Wb of each center land portion 31A, 31B is between 70% and 100% of the value obtained by dividing the width Wa of the center portion 31 by the number of center land portions 31A, 31B. By defining it in this way, the rigidity becomes constant in each center land portion 31A, 31B, and the low rolling resistance performance is improved. In order to obtain the above effect, it is preferable that the width Wb of each center land portion 31A, 31B is divided equally in this pneumatic tire 1.

[0047] Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 2, in the center land portions 31A and 31B, the dimension P of one pitch in the tire circumferential direction of the widthwise narrow groove 40 and the dimension Wb in the tire width direction of the center land portions 31A and 31B satisfy the relationship 0.3 ≤ P / Wb ≤ 0.8.

[0048] With this pneumatic tire 1, by setting the pitch P in the tire circumferential direction of the narrow grooves 40 in the width direction to a specified range with respect to the tire width direction dimension Wb of the center land portion 31A, 31B, the wet performance can be improved by the arrangement of the narrow grooves 40 in the width direction, while ensuring the rigidity of the center land portion 31A, 31B and minimizing the impact on low rolling resistance performance. In order to obtain the above effect, it is preferable that this pneumatic tire 1 satisfies the relationship 0.4 ≤ P / Wb ≤ 0.7. Note that there are multiple types (for example, three types of pitches) for the pitch P in the tire circumferential direction of the narrow grooves 40 in the width direction.

[0049] Furthermore, in the pneumatic tire 1 of this embodiment, multiple circumferential grooves 22 are arranged in the center portion 31, and the chamfered portion 50 is positioned at the groove opening 20a on the circumferential main groove 21 side of each circumferential groove 22 on the outermost side in the tire width direction.

[0050] With this pneumatic tire 1, by placing a chamfered portion 50 at the groove opening 20a on the circumferential main groove 21 side of the circumferential narrow groove 22, rigidity can be ensured without the chamfered portion 50 on the central side of the center portion 31 in the tire width direction, thereby maintaining lower rolling resistance performance, while improving wet performance on the outer side of the center portion 31 in the tire width direction.

[0051] Furthermore, in the pneumatic tire 1 of this embodiment, the chamfered portion 50 has a plurality of shallow, fine grooves 50a arranged on its surface.

[0052] According to this pneumatic tire 1, by providing shallow, narrow grooves 50a on the surface of the chamfered portion 50, the groove volume including the chamfered portion 50 is increased, improving wet performance.

[0053] Furthermore, in the pneumatic tire 1 of the embodiment, the center land portion 31A, 31B includes an R-chamfered portion 60 that is positioned from at least one groove opening 20a of the circumferential groove 22 to the groove opening 40a of the widthwise groove 40 on the higher angle side L of the angle formed by the widthwise narrow grooves 40 whose openings 40o face each other with respect to the circumferential narrow groove 22.

[0054] According to this pneumatic tire 1, having an R-chamfered portion 60 increases the groove volume in addition to providing a chamfered portion 50, resulting in improved wet performance.

[0055] Furthermore, the pneumatic tire 1 of this embodiment includes shallow grooves 71 and 72 located in the shoulder portions 32 that are partitioned on the outer side in the tire width direction of each circumferential main groove 21 at the outermost edge in the tire width direction.

[0056] According to this pneumatic tire 1, by arranging shallow grooves 71 and 72, the contact pressure with the center section 31 is made uniform, improving low rolling resistance performance.

[0057] By the way, in this embodiment, as described above, a pneumatic tire 1 was described as an example of a tire. This 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 this embodiment can be arbitrarily applied to other tires within the scope of what is obvious to those skilled in the art. Other tires include, for example, airless tires and solid tires. [Examples]

[0058] Figures 8 and 9 are charts showing the results of performance tests of the pneumatic tire according to the embodiment. Below, we will describe the performance evaluation tests conducted on the conventional pneumatic tire, the comparative pneumatic tire, and the pneumatic tire according to the embodiment. The performance evaluation tests included tests for low rolling resistance performance and wet performance.

[0059] The low rolling resistance performance evaluation test involves mounting a pneumatic tire (test tire) of size 275 / 70R22.5 onto a specified rim (22.5 x 8.25), applying the specified air pressure, and mounting it on a heavy-duty vehicle. Under test conditions compliant with UN R117-04 (UN Regulation No. 117 Revision 4), the rolling resistance coefficient (ratio of rolling resistance to load on the test tire) is measured. Based on this measurement result, an index evaluation is performed using the reciprocal, with the conventional example as the baseline (100). A higher value in this evaluation is preferable.

[0060] The wet performance evaluation test involves mounting a pneumatic tire of the above size (test tire) onto a specified rim, applying the specified air pressure, and mounting it on a heavy-duty vehicle. A braking test is then conducted on a wet surface with a water depth of 1 mm under test conditions compliant with UN R117-04 (UN Regulation No. 117 Revision 4), and the braking distance is measured. Based on this measurement result, an index evaluation is performed using the reciprocal, with the conventional example as the baseline (100). A higher numerical value in this evaluation is preferable.

[0061] Conventional pneumatic tires have two circumferential main grooves as shown in Figure 2, but lack circumferential and widthwise narrow grooves, and therefore do not have chamfered edges.

[0062] The pneumatic tire of Comparative Example 1 has two circumferential main grooves as shown in Figure 2 and two circumferential fine grooves in the center, but does not have widthwise fine grooves or chamfered edges. The pneumatic tire of Comparative Example 2 has two circumferential main grooves as shown in Figure 2 and has widthwise fine grooves but no circumferential fine grooves, but does not have chamfered edges. The pneumatic tire of Comparative Example 3 has two circumferential main grooves as shown in Figure 2, two circumferential fine grooves in the center, and widthwise fine grooves, but does not have chamfered edges.

[0063] The pneumatic tire of the embodiment has two circumferential main grooves, two circumferential narrow grooves in the center, a widthwise narrow groove, and a chamfered portion, as shown in Figure 2.

[0064] As shown in the test results, the pneumatic tire of this embodiment shows improved low rolling resistance and wet performance compared to the conventional and comparative examples.

[0065] This disclosure includes the following inventions: [Invention 1] On the tread surface, At least two circumferential main grooves extending along the circumferential direction of the tire, A center portion is partitioned between each of the circumferential main grooves on the outermost side in the tire width direction, In the aforementioned center portion, a circumferential narrow groove is provided that extends along the circumferential direction of the tire and has a narrower groove width than the circumferential main groove, In the aforementioned center portion, the center land portion is partitioned by the circumferential main groove and the circumferential narrow groove, In the aforementioned center land portion, both ends extending along the tire width direction open into the circumferential main groove or the circumferential narrow groove, and multiple such grooves are arranged in the circumferential direction of the tire, and the angle of the openings facing each other with respect to the center line of the circumferential narrow groove changes, and the widthwise narrow grooves are narrower than the circumferential main groove, In the aforementioned center land portion, a chamfered portion is provided on the low-angle side of each of the widthwise narrow grooves facing each other with respect to the circumferential narrow groove, extending from at least one groove opening of the circumferential narrow groove to the groove opening of the widthwise narrow groove, Tires, including. [Invention 2] The aforementioned widthwise narrow groove includes a first widthwise narrow groove with a relatively wide groove width and a second widthwise narrow groove with a relatively narrow groove width. In the aforementioned center land portion, the first widthwise narrow groove and the second widthwise narrow groove are arranged in a mixed manner in the tire circumferential direction. The tire described in Invention 1. [Invention 3] The aforementioned narrow groove in the width direction includes a first narrow groove in the width direction that has a relatively wide groove width and a relatively deep groove depth and has sipes at the bottom of the groove, and a second narrow groove in the width direction that has a relatively narrow groove width and a relatively shallow groove depth. In the aforementioned center land portion, the first widthwise narrow groove and the second widthwise narrow groove are arranged in a mixed manner in the tire circumferential direction. The tire described in Invention 1. [Invention 4] The chamfered portion is formed so that it gradually narrows in width and depth as it moves away from the narrow groove in the width direction along the circumferential groove. A tire according to any one of inventions 1 to 3. [Invention 5] The dimension Wa in the tire width direction of the center portion, the dimension Wb in the tire width direction of the center land portion, and the number of circumferential grooves A satisfy the relationship 0.7 ≤ Wb(A+1) / Wa < 1.0. A tire according to any one of inventions 1 to 4. [Invention 6] In the aforementioned center land portion, the dimension P of one pitch in the tire circumferential direction of the widthwise narrow groove and the dimension Wb in the tire widthwise direction of the aforementioned center land portion satisfy the relationship 0.3 ≤ P / Wb ≤ 0.8. A tire according to any one of inventions 1 to 5. [Invention 7] In the center portion, a plurality of circumferential grooves are arranged, and the chamfered portion is positioned at the groove opening on the circumferential main groove side of each of the outermost circumferential grooves in the tire width direction. A tire according to any one of inventions 1 to 6. [Invention 8] The chamfered portion has a plurality of shallow grooves arranged on its surface. A tire according to any one of inventions 1 to 7. [Invention 9] In the aforementioned center land portion, an R-chamfered portion is provided, which is located on the higher angle side of the angle formed by each of the widthwise narrow grooves whose openings face each other with respect to the circumferential narrow groove, extending from at least one groove opening of the circumferential narrow groove to the groove opening of the circumferential narrow groove, A tire according to any one of inventions 1 to 8. [Invention 10] This includes shallow grooves located in the shoulder portions that are partitioned on the outer side in the tire width direction of each of the circumferential main grooves on the outermost side in the tire width direction, A tire according to any one of inventions 1 to 9. [Explanation of Symbols]

[0066] 1. Pneumatic tire (tire) 15A Tread surface 21 Circumferential main groove 22 Circumferential thin groove 20a groove opening 31 Center Section 31A, 31B Center Track and Field Club 32 Shoulder section 40 Width direction thin groove 40a groove opening 40b groove bottom 40o opening 41 First width direction thin groove 41B Sipe 42 Second widthwise narrow groove 50 Chamfer 50a Shallow groove 60 R chamfer 71, 72 Shallow groove

Claims

1. On the tread surface, At least two circumferential main grooves extending along the circumferential direction of the tire, A center portion is partitioned between each of the circumferential main grooves on the outermost side in the tire width direction, In the aforementioned center portion, a circumferential narrow groove is provided that extends along the circumferential direction of the tire and has a narrower groove width than the circumferential main groove, In the aforementioned center portion, the center land portion is partitioned by the circumferential main groove and the circumferential narrow groove, In the aforementioned center land portion, both ends extending along the tire width direction open into the circumferential main groove or the circumferential narrow groove, and multiple such grooves are arranged in the circumferential direction of the tire, and the angle of the openings facing each other with respect to the center line of the circumferential narrow groove changes, and the widthwise narrow grooves are narrower than the circumferential main groove, In the aforementioned center land portion, a chamfered portion is provided on the low-angle side of each of the widthwise narrow grooves facing each other with respect to the circumferential narrow groove, extending from at least one groove opening of the circumferential narrow groove to the groove opening of the widthwise narrow groove, Tires, including.

2. The aforementioned widthwise narrow groove includes a first widthwise narrow groove with a relatively wide groove width and a second widthwise narrow groove with a relatively narrow groove width. In the aforementioned center land portion, the first widthwise narrow groove and the second widthwise narrow groove are arranged in a mixed manner in the tire circumferential direction. The tire according to claim 1.

3. The aforementioned narrow groove in the width direction includes a first narrow groove in the width direction that has a relatively wide groove width and a relatively deep groove depth and has sipes at the bottom of the groove, and a second narrow groove in the width direction that has a relatively narrow groove width and a relatively shallow groove depth. In the aforementioned center land portion, the first widthwise narrow groove and the second widthwise narrow groove are arranged in a mixed manner in the tire circumferential direction. The tire according to claim 1.

4. The chamfered portion is formed so that it gradually narrows in width and depth as it moves away from the narrow groove in the width direction along the circumferential groove. The tire according to claim 1.

5. The dimension Wa in the tire width direction of the center portion, the dimension Wb in the tire width direction of the center land portion, and the number of circumferential grooves A satisfy the relationship 0.7 ≤ Wb(A+1) / Wa < 1.

0. The tire according to claim 1.

6. In the aforementioned center land portion, the dimension P of one pitch in the tire circumferential direction of the widthwise narrow groove and the dimension Wb in the tire widthwise direction of the aforementioned center land portion satisfy the relationship 0.3 ≤ P / Wb ≤ 0.

8. The tire according to claim 1.

7. In the center portion, a plurality of circumferential grooves are arranged, and the chamfered portion is positioned at the groove opening on the circumferential main groove side of each of the outermost circumferential grooves in the tire width direction. The tire according to claim 1.

8. The chamfered portion has a plurality of shallow grooves arranged on its surface. The tire according to claim 1.

9. In the aforementioned center land portion, an R-chamfered portion is provided, which is located on the higher angle side of the angle formed by each of the widthwise narrow grooves whose openings face each other with respect to the circumferential narrow groove, extending from at least one groove opening of the circumferential narrow groove to the groove opening of the circumferential narrow groove, The tire according to claim 1.

10. This includes shallow grooves located in the shoulder portions that are partitioned on the outer side in the tire width direction of each of the circumferential main grooves on the outermost side in the tire width direction, The tire according to claim 1.

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