Tire for heavy load

Abstract

To provide a tire 2 for a heavy load which can suppress occurrence of tread breakage when being released from a mold, and deterioration of wet performance by wear, and can achieve reduction in rolling resistance.SOLUTION: A tire 2 includes a tread 4. The tread 4 includes a plurality of circumferential grooves 10, and a plurality of crossing sipes 12. The plurality of circumferential grooves 10 includes a plurality of circumferential main grooves 14 and one or more circumferential fine grooves 16. The plurality of crossing sipes 12 connects the circumferential main grooves 14 and the circumferential fine grooves 16. The circumferential fine groove 16 includes a fine groove part 52, a wide expansion part 54, and an inflection part 56. The tread 4 is grounded with the road surface and is deformed, and thereby a pair of groove walls 16 possessed by the circumferential fine grooves 16 is brought into contact with each other in the fine groove part 52. The maximum width W2 of the wide expansion part 54 is wider than the minimum width W1 of the fine groove part 52. The contour of the inflection part 56 is represented by a circular arc having a radius R1, and the radius R1 is larger than the height HW2 which is a half of the maximum width W2 of the wide expansion part 54.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] The tire tread has a plurality of circumferential grooves arranged in parallel in the axial direction, which define a plurality of land portions in the tread. The land portion of a tire deforms when it comes into contact with the road surface. This deformation of the land portion affects the tire's rolling resistance. Considering the impact on the environment, there is a strong demand for tires to reduce rolling resistance. By providing narrow groove portions with narrow groove widths in the circumferential grooves, the land portions can support each other when the tread comes into contact with the road surface, thereby suppressing deformation of the land portions. In order to reduce the rolling resistance of a tire, the use of circumferential grooves having narrow groove portions, that is, narrow circumferential grooves, has been considered (for example, Patent Document 1 listed below).

[0003] A tire is made by curing a green tire in a mold. The tread ring of the mold forms the outer surface of the tread. If the tread has circumferential grooves, the tread ring has ridges that mirror the shape of the circumferential grooves. The ridges project radially inward.

[0004] When the mold is a split mold, the tread ring is made up of a plurality of segments arranged in the circumferential direction. Once the vulcanization process is complete, the tire is released from the mold, and each segment is moved radially outward, pulling the ridges out of the tread.

[0005] The circumferential narrow grooves also affect, for example, the running performance on wet roads (hereinafter also referred to as wet performance). Improvements to the circumferential narrow grooves are being made while taking into consideration the influence on various performances. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-094891 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a heavy-duty tire that can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve reduced rolling resistance. [Means for solving the problem]

[0008] The heavy-duty tire according to the present invention has a tread that comes into contact with a road surface. The tread has a tread pattern including a plurality of circumferential grooves extending continuously in the circumferential direction and a plurality of transverse sipes aligned in the circumferential direction. The plurality of circumferential grooves include a plurality of circumferential main grooves and one or more circumferential narrow grooves. Each of the plurality of circumferential main grooves has a pair of groove walls that do not come into contact with the road surface even when the tread comes into contact with the road surface and deforms. The plurality of circumferential main grooves define a plurality of land portions aligned in the axial direction in the tread. The plurality of land portions include two shoulder land portions located at the outermost sides in the axial direction and one or more main land portions located between the two shoulder land portions. Each of the one or more main land portions includes the circumferential narrow groove. The circumferential narrow groove defines two main narrow land portions in the main land portion, thereby defining a plurality of main narrow land portions in the tread. At least one of the plurality of main narrow land portions includes a plurality of transverse sipes. The multiple transverse sipes connect the circumferential main groove and the circumferential narrow groove. The circumferential narrow groove includes a narrow groove portion including the groove mouth of the circumferential narrow groove, a widened portion including the groove bottom of the circumferential narrow groove, and an inflection portion connecting the narrow groove portion and the widened portion. When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove contact each other at the narrow groove portion. The maximum width W2 of the widened portion is wider than the minimum width W1 of the narrow groove portion. In a cross section of the circumferential narrow groove along a plane perpendicular to the length direction of the circumferential narrow groove, the outline of the inflection portion is represented by an arc having a radius R1, and the radius R1 is greater than a length HW2 that is half the maximum width W2 of the widened portion. [Effects of the Invention]

[0009] According to the present invention, a heavy-duty tire can be obtained that can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve reduced rolling resistance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a development view showing a tread of a heavy duty tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is an enlarged development view showing a part of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 4 is a cross-sectional view taken along line VV in FIG. [Figure 6] 1A to 1C are cross-sectional views illustrating a method for manufacturing a tire. [Figure 7] FIG. 10 is a cross-sectional view showing a modified example of the circumferential narrow groove. [Figure 8] FIG. 10 is a cross-sectional view showing another modified example of the circumferential narrow groove. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0012] The tire of the present invention is mounted on a rim. The inside of the tire is filled with air, and the internal pressure of the tire is adjusted. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly includes a rim and a tire mounted on the rim.

[0013] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state.

[0014] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part of the tire's meridian cross section, which cannot be measured when the tire is mounted on a regular rim, are measured on a cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads of the tire mounted on a regular rim. Note that the tire configuration, which cannot be confirmed when the tire is mounted on a regular rim, is confirmed on the cut surface.

[0015] A genuine rim is a rim specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are all genuine rims.

[0016] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0017] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0018] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0019] [Findings that form the basis of the present invention] As mentioned above, by providing narrow circumferential grooves in the tread, deformation of the land portion when the tread comes into contact with the road surface is suppressed. By making some of the circumferential grooves in the tread narrow circumferential grooves, the rolling resistance of the tire can be reduced. Circumferential narrow grooves have poorer drainage than circumferential main grooves, and if some of the circumferential grooves in the tread are made into circumferential narrow grooves, there is a concern that wet performance will deteriorate as the tread wears. Sipes that cross the land area (hereinafter referred to as "transverse sipes") can function as edge components. By providing transverse sipes on the land area, the tire can suppress a decline in wet performance. By providing a widened portion with a groove width wider than the narrow groove portion on the groove bottom side of the circumferential narrow groove, the widened portion can contribute to ensuring groove volume. By exposing the widened portion, the tire can suppress a decrease in wet performance.

[0020] As described above, when circumferential narrow grooves are formed in the tread, the tread ring of the mold is provided with ridges that reflect the shape of the circumferential narrow grooves. When widened portions are provided in the circumferential narrow grooves, the shape of the widened portions is reflected in the tip portions of the ridges. When the tire is released from the mold after the vulcanization process is completed, the tip portions pass through the narrow grooves, which are narrower than the widened portions. Pulling out the ridges involves deformation of the land portions.

[0021] Blades are used to cut sipes into the tread. For example, when forming a tread pattern in which transverse sipes are connected to circumferential narrow grooves, a mold is used in which the blades for the transverse sipes are connected to the ridges for the circumferential narrow grooves. When a tire is manufactured using such a mold, when the ridges and blades are pulled out of the tread, part of the land portion tends to get caught on the connection between the ridge and the blade. When the mold is a split mold, the closer the ridges and blades are to the circumferential end of the segment, the more obliquely they are pulled out relative to their protruding direction. Stress tends to concentrate in the land portion located near the connection. Depending on the degree of stress concentration, there is a concern that chips may occur in the land portion, i.e., the tread.

[0022] Therefore, the inventors have conducted extensive research into the shape of circumferential narrow grooves in order to obtain a tire that can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and achieve reduced rolling resistance, and have completed the present invention, which will be described below.

[0023] [Outline of the embodiment of the present invention] The present invention relates to a tire having a tread that comes into contact with a road surface, the tread having a tread pattern including a plurality of circumferential grooves that extend continuously in the circumferential direction and a plurality of transverse sipes that are aligned in the circumferential direction, the plurality of circumferential grooves including a plurality of circumferential main grooves and one or more circumferential narrow grooves, each of the plurality of circumferential main grooves having a pair of groove walls that do not come into contact even when the tread comes into contact with the road surface and deforms, the plurality of circumferential main grooves configuring a plurality of land portions that are aligned in the axial direction in the tread, the plurality of land portions including two shoulder land portions located at the outermost sides in the axial direction and one or more main land portions located between the two shoulder land portions, each of the one or more main land portions including the circumferential narrow groove, and the circumferential narrow groove configuring two main narrow land portions in the main land portions, thereby configuring a plurality of main narrow land portions in the tread. and at least one main narrow land portion among the plurality of main narrow land portions is provided with the plurality of transverse sipes, the plurality of transverse sipes connecting the circumferential main groove and the circumferential narrow groove, the circumferential narrow groove including a narrow groove portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and an inflection portion connecting the narrow groove portion and the widened portion, the tread comes into contact with the road surface and deforms, causing a pair of groove walls of the circumferential narrow groove to come into contact with each other at the narrow groove portion, a maximum width W2 of the widened portion is wider than a minimum width W1 of the narrow groove portion, and in a cross section of the circumferential narrow groove along a plane perpendicular to the longitudinal direction of the circumferential narrow groove, an outline of the inflection portion is represented by an arc having a radius R1, and the radius R1 is greater than a length HW2 that is half the maximum width W2 of the widened portion.

[0024] The heavy-duty tire of the present invention can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve reduced rolling resistance. The mechanism by which such effects are achieved has not been clarified, but is presumed to be as follows.

[0025] When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other at the narrow groove portion. The two land portions located on both sides of the circumferential narrow groove support each other, suppressing deformation of the land portions. This tire can reduce rolling resistance. The transverse sipes act as edge components, allowing the tire to maintain good wet performance even as the tread wears. The widened portion provided on the bottom side of the circumferential narrow groove contributes to ensuring groove volume. Even if the transverse sipes disappear due to tread wear, the exposed widened portion contributes to maintaining wet performance. This tire will maintain good wet performance from new until the tire needs replacing. This tire can suppress deterioration of wet performance due to wear and achieve reduced rolling resistance.

[0026] The mold for this tire is provided with ridges that form circumferential narrow grooves and blades that form transverse sipes, and the tip portions of the ridges form the widened portions of the circumferential narrow grooves. Once the vulcanization process is complete, the tire is released from the mold, at which point the ridges and blades are pulled out from the tread.

[0027] In this tire, the contour of the portion between the narrow groove portion and the widened portion, i.e., the inflection portion, is represented by an arc with a large radius R1. The shape of the inflection portion is configured so that the groove width gradually widens from the narrow groove portion toward the widened portion. When the ridges and blades are pulled out of the tread, the land portion is less likely to get caught at the connection portion between the ridges and blades. Stress concentration at the connection portion between the circumferential narrow groove and the transverse sipe is suppressed. This tire can suppress the occurrence of tread chipping when the tire is released from the mold. This tire can suppress the occurrence of tread chipping when the tire is released from the mold and the deterioration of wet performance due to wear, thereby achieving reduced rolling resistance.

[0028] Preferably, the ratio W1 / W2 of the minimum width W1 of the narrow groove portion to the maximum width W2 of the widened portion is 0.15 or more and 0.35 or less. In this case, the tire can effectively suppress the occurrence of tread chipping and the deterioration of wet performance due to wear.

[0029] Preferably, the narrow groove has a minimum width W1 of 2.5 mm or less. In this case, the tire can effectively reduce rolling resistance.

[0030] Preferably, in a cross section of the circumferential narrow groove along a plane perpendicular to the longitudinal direction of the circumferential narrow groove, the outline of the widened portion is represented by an arc having a radius R2, and the ratio R1 / R2 of the radius R1 of the arc representing the outline of the inflection portion to the radius R2 of the arc representing the outline of the widened portion is 1.5 or more. In this case, the tire can effectively suppress the occurrence of tread chipping.

[0031] Preferably, a ratio D2 / D1 of a groove depth D2 of the narrow groove portion to a groove depth D1 of the circumferential narrow groove is equal to or greater than 0.25 and is equal to or less than 0.70. In this case, the tire can effectively suppress the occurrence of tread chipping and effectively reduce rolling resistance.

[0032] Preferably, a groove depth D3 from the groove opening of the circumferential narrow groove to a position where the widened portion has a maximum width W2, a groove depth D4 of the transverse sipe, and a groove depth D2 of the narrow groove portion satisfy the following formula: D2≦D4≦D3 In this case, the tire can effectively suppress the occurrence of tread chipping and the deterioration of wet performance due to wear, and can effectively reduce rolling resistance.

[0033] Preferably, the angle formed by the transverse sipe with respect to the axial direction is equal to or greater than −35 degrees and equal to or less than 35 degrees. In this case, the tire can effectively suppress the occurrence of tread chipping.

[0034] Preferably, the tread pattern includes a plurality of pitch patterns arranged in a circumferential direction and having the same circumferential length, and the plurality of pitch patterns have the same pattern as each other, A ratio L / L1 of a circumferential length L of the pitch pattern to an interval L1 between two transverse sipes aligned in the circumferential direction is 1.0 or more and 3.5 or less. In this case, the tire can effectively suppress the occurrence of tread chipping and the deterioration of wet performance due to wear, and can effectively reduce rolling resistance.

[0035] [Details of the embodiment of the present invention] FIG. 1 is a plan view showing a portion of a tread 4 of a tire 2 according to one embodiment of the present invention in which the tire 2 is developed. The tire 2 is mounted on vehicles such as trucks and buses. The tire 2 is a heavy-duty tire. The tread 4 comes into contact with the road surface. The tire 2 has a tread 4 that comes into contact with the road surface.

[0036] In FIG. 1, the direction indicated by the double arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis (not shown) of the tire 2. The direction indicated by the double arrow CD is the circumferential direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the radial direction of the tire 2. In FIG. 1, the dashed dotted line EL extending in the circumferential direction represents the equatorial plane of the tire 2. 1, the side indicated by arrow AD1 is the first axial direction side of the tire 2, and the side indicated by arrow AD2 is the second axial direction side of the tire 2. The side facing the equatorial plane in the axial direction is the axially inner side, and the side facing the edge of the tread surface described later is the axially outer side. In FIG. 1, the side indicated by the arrow CD1 is the first circumferential direction side of the tire 2, and the side indicated by the arrow CD2 is the second circumferential direction side of the tire 2.

[0037] Fig. 1 shows a tread pattern configured on a tread 4. Using this tread pattern as an example, the tread pattern of the present invention will be described. In the present invention, the internal structure of the tire 2 is not particularly important. Although not described in detail, this tire 2 has a general internal structure as the internal structure of a heavy-duty tire. The tread pattern in FIG. 1 is that of a new tire 2, that is, an unworn tread 4.

[0038] The tread 4 is located on the radially outer side of the tire 2 and extends in the circumferential direction. The outer peripheral surface of the tread 4 is a tread surface 6. The tread 4 has the tread surface 6. The tire 2 comes into contact with the road surface at the tread surface 6. The tread 4 is made of cross-linked rubber. Although not described in detail, the portion of the tread 4 including the tread surface 6 is made of cross-linked rubber that takes into consideration wear resistance and grip performance. The other portions are made of low-heat-generating cross-linked rubber. Grooves 8 are cut into the tread 4. This forms a tread pattern. The tread 4 has a tread pattern.

[0039] The intersection of the tread surface 6 and the equatorial plane is the equator Eq. When the grooves 8 are located on the equatorial plane, the equator Eq is determined based on a virtual tread surface obtained by assuming that the grooves 8 are not on the equatorial plane. The equator Eq is the radially outer end of the tire 2.

[0040] The solid line indicated by the symbol TE is the edge of the tread surface 6 . In the present invention, when the edge TE of the tread surface 6 cannot be identified visually, the position on the outer surface of the tire corresponding to the axially outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and bringing the tire into contact with a flat surface is represented as the edge of the tread surface.

[0041] 1, the end TE of the tread surface 6 located on the first axial direction AD1 side is the first end TE1. Although not shown, the end TE located on the second axial direction AD2 side is the second end TE2. The length indicated by the double arrow TW is the width of the tread surface 6. The width TW of the tread surface 6 is the axial distance from a first end TE1 to a second end TE2 of the tread surface 6. The width TW of the tread surface 6 is expressed as the length measured along the tread surface 6.

[0042] Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 2 shows a cross-section of a groove 8, more specifically, a circumferential main groove (more specifically, a crown circumferential main groove) described later. The main configuration of the groove 8 will be described based on Fig. 2. 2, the direction indicated by the double-headed arrow RD is the radial direction of the tire 2. The side indicated by the arrow RD1 is the radially outer side of the tire 2, and the side indicated by the arrow RD2 is the radially inner side of the tire 2. In the present invention, the cross section of the groove 8 is represented by a cross section along a plane perpendicular to the longitudinal direction of the groove 8.

[0043] The groove 8 has a pair of groove walls 8W that bridge between the groove mouth 8M and the groove bottom 8T. The pair of groove walls 8W, the first groove wall 8W and the second groove wall 8W, face each other. The groove width of the groove 8 is expressed as the distance between the opposing first groove wall 8W and second groove wall 8W, i.e., the groove wall distance. The length indicated by the double-headed arrow WG in Figure 2 is the groove width of the groove 8 at the groove mouth 8M. The groove width WG is expressed as the shortest distance between a pair of edges 8E that form the groove mouth 8M. If the groove mouth 8M of the groove 8 is machined to have a tapered shape, the groove width at the groove mouth 8M of the groove 8 is expressed based on a virtual edge obtained by assuming that the groove is not machined to have a tapered shape. The length indicated by the double-headed arrow DG is the depth of the groove 8. The depth DG of the groove 8 is expressed as the shortest distance from the line segment connecting the left and right edges 8E to the groove bottom 8T of the groove 8. The position, groove width WG, and groove depth DG of the groove 8 are determined appropriately according to the specifications of the tire 2.

[0044] The groove bottom 8T is the deepest position in the cross section of the groove 8. The distance from the line segment connecting the left and right edges 8E that make up the groove opening 8M to the groove 8 is measured along the normal to this line segment. The position where the distance from this line segment to the groove 8 is greatest is the groove bottom 8T. Of the groove 8, the portion including the groove bottom 8T is also referred to as the bottom surface 8B. The bottom surface 8B shown in FIG. 2 is a curved surface. This bottom surface 8B may be configured as a flat surface. In this case, the center of the width of the flat surface that configures the bottom surface 8B is used as the groove bottom 8T.

[0045] A groove 8 having a groove width WG of less than 1.0 mm at its groove mouth 8M is called a sipe. A groove 8 other than a sipe is also called a normal groove, and has a groove width WG of 1.0 mm or more at its groove mouth 8M. The sipe may include a portion having a groove width of 1.0 mm or more between the groove mouth 8M and the groove bottom 8T (hereinafter referred to as a portion equivalent to a normal groove). In this case, as the tread 4 wears and the portion equivalent to a normal groove becomes exposed, the sipe changes into a normal groove. The normal groove may include a portion (a portion corresponding to a sipe) having a groove width of less than 1.0 mm between the groove mouth 8M and the groove bottom 8T. In this case, the normal groove changes into a sipe when the tread 4 wears and the portion corresponding to the sipe becomes exposed. Even among normal grooves, normal grooves that have a narrow groove width and allow a pair of groove walls 8W to come into contact with each other when the tread 4 comes into contact with the road surface and deforms are also called narrow grooves. Narrow grooves have a pair of groove walls 8W that come into contact with each other when the tread 4 comes into contact with the road surface and deforms. In contrast, normal grooves that have a wide groove width and do not allow a pair of groove walls 8W to come into contact with each other even when the tread 4 comes into contact with the road surface and deforms are also called main grooves. Main grooves have a pair of groove walls 8W that do not come into contact with each other even when the tread 4 comes into contact with the road surface and deforms.

[0046] The tread 4 is formed with a plurality of circumferential grooves 10 and a plurality of transverse sipes 12. Each of the plurality of circumferential grooves 10 extends continuously in the circumferential direction. The circumferential grooves 10 are the normal grooves described above. The plurality of transverse sipes 12 are aligned in the circumferential direction. Each of the plurality of transverse sipes 12 crosses a main narrow land portion, which will be described later. The transverse sipes 12 are the sipes described above. The tread pattern of the tire 2 includes a plurality of circumferential grooves 10 and a plurality of transverse sipes 12 .

[0047] The multiple circumferential grooves 10 include multiple circumferential main grooves 14 and one or more circumferential narrow grooves 16. The tread 4 shown in Fig. 1 has three circumferential main grooves 14 and two circumferential narrow grooves 16. The tread 4 may have four or more circumferential main grooves 14 and three or more circumferential narrow grooves 16.

[0048] 2, the circumferential main groove 14 has a pair of groove walls 14W that bridge between the groove mouth 14M and the groove bottom 14T. The portion of the circumferential main groove 14 that includes the groove bottom 14T is also referred to as a bottom surface 14B. The circumferential main groove 14 is the aforementioned main groove. A pair of groove walls 14W of the circumferential main groove 14 do not come into contact with each other even when the tread 4 comes into contact with the road surface and deforms. In other words, the circumferential main groove 14 has a pair of groove walls 14W that do not come into contact with each other even when the tread 4 comes into contact with the road surface and deforms.

[0049] The length indicated by the double-headed arrow DGm in FIG. 2 is the groove depth of the circumferential main groove 14. The groove depth DGm of the circumferential main groove 14 is, for example, 10 mm or more and 21 mm or less. From the viewpoint of enabling the tire 2 to exhibit good wet performance, the groove depth DGm is preferably 13 mm or more and 18 mm or less. As will be described later, the groove depth of the circumferential narrow groove 16 is the same as the groove depth DGm of the circumferential main groove 14 or is shallower than the groove depth DGm of the circumferential main groove 14.

[0050] As described above, three circumferential main grooves 14 are formed in the tread 4. Of the three circumferential main grooves 14, the circumferential main groove 14 located on the axially outermost side is the shoulder circumferential main groove 18. The circumferential main groove 14 located on the axially innermost side, in other words, the circumferential main groove 14 located on the equatorial plane or the circumferential main groove 14 closest to the equatorial plane, is the crown circumferential main groove 20. In the tread 4 shown in FIG. 1 , of the three circumferential main grooves 14, the circumferential main groove 14 located on the axially innermost side is located on the equatorial plane. This circumferential main groove 14 located on the equatorial plane is the crown circumferential main groove 20. The tread 4 includes a crown circumferential main groove 20 and a pair of shoulder circumferential main grooves 18. Although not shown, a circumferential main groove 14 may be provided between the crown circumferential main groove 20 and the shoulder circumferential main groove 18. In this case, the circumferential main groove 14 located between the crown circumferential main groove 20 and the shoulder circumferential main groove 18 is also called a middle circumferential main groove.

[0051] 1, the length indicated by the double arrow WGmc is the groove width at the groove mouth 20M of the crown circumferential main groove 20. The length indicated by the double arrow WGms is the groove width at the groove mouth 18M of the shoulder circumferential main groove 18.

[0052] The ratio (WGmc / TW) of the groove width WGmc of the crown circumferential main groove 20 to the width TW of the tread surface 6 exceeds 2.0%. Specifically, the ratio (WGmc / TW) is preferably 4.0% or more and 10% or less. 1, the groove width WGms of the shoulder circumferential main groove 18 is wider than the groove width WGmc of the crown circumferential main groove 20. The ratio (WGms / TW) of the groove width WGms of the shoulder circumferential main groove 18 to the width TW of the tread surface 6 is preferably 5.0% or more and 11% or less.

[0053] As shown in Fig. 1, a bottom surface 20B of the crown circumferential main groove 20 is provided with a protrusion 22 protruding from the bottom surface 20B. A plurality of the protrusions 22 are arranged at predetermined intervals in the circumferential direction. The protrusions 22 prevent stones from getting caught in the crown circumferential main groove 20.

[0054] A plurality of circumferential main grooves 14 are formed in the tread 4 of this tire 2, and a plurality of land portions 24 are arranged in the axial direction. The plurality of circumferential main grooves 14 form a plurality of land portions 24 in the tread 4. The tread 4 shown in FIG. 1 has three circumferential main grooves 14, and four land portions 24 are formed.

[0055] Of the multiple land portions 24, the land portion 24 located at the outermost position in the axial direction is a shoulder land portion 26. The shoulder land portion 26 includes an edge TE of the tread surface 6. The land portion 24 located at the innermost position in the axial direction, in other words, the land portion 24 located on the equatorial plane or the land portion 24 closest to the equatorial plane, is a crown land portion 28. In the tread 4 shown in FIG. 1 , of the four land portions 24, the land portion 24 located at the innermost position in the axial direction is closest to the equatorial plane. This land portion 24 closest to the equatorial plane is the crown land portion 28. The tread 4 includes a pair of crown land portions 28 and a pair of shoulder land portions 26. Although not shown, a land portion 24 may be provided between the crown land portion 28 and the shoulder land portion 26. In this case, the land portion 24 located between the crown land portion 28 and the shoulder land portion 26 is also called a middle land portion.

[0056] In the present invention, the land portion 24 located between the two shoulder land portions 26 is the main land portion 30 . 1, the land portion 24 located between the two shoulder land portions 26 is a crown land portion 28. The crown land portion 28 of this tire 2 is a main land portion 30.

[0057] The tread 4 of this tire 2 is configured with a plurality of land portions 24, and the plurality of land portions 24 include two shoulder land portions 26 located at the axially outermost positions and one or more main land portions 30 located between the two shoulder land portions 26. In the tread 4 shown in Fig. 1, two crown land portions 28 are located between two shoulder land portions 26. The plurality of land portions 24 formed in this tread 4 includes two shoulder land portions 26 and two main land portions 30.

[0058] 1 is the width of the shoulder land portion 26. In this tire 2, when the width of the land portion 24 varies in the circumferential direction, the width of the land portion 24 is represented by the maximum width. In the shoulder land portion 26 of the tire 2, the ratio (WLS / TW) of the maximum width WLS to the width TW of the tread surface 6 is equal to or greater than 15% and equal to or less than 25%.

[0059] The shoulder land portion 26 is formed with lateral shallow grooves 32 and longitudinal shallow grooves 34. The shoulder land portion 26 may be formed as a plain land portion without any grooves 8. The shoulder land portion 26 may be formed with the above-mentioned sipes or fine grooves.

[0060] 1 has a plurality of lateral shallow grooves 32. The plurality of lateral shallow grooves 32 are aligned in the circumferential direction. The tread pattern of the tire 2 may include a plurality of lateral shallow grooves 32 aligned in the circumferential direction. Each of the multiple lateral shallow grooves 32 connects between the shoulder circumferential main groove 18 and the edge TE of the tread surface 6. As shown in FIG. 1 , the lateral shallow grooves 32 are inclined with respect to the axial direction. The axially inner ends of the lateral shallow grooves 32 are located closer to the second circumferential direction than the axially outer ends. Although not described in detail, the lateral shallow grooves 32 have a groove width similar to that of the aforementioned narrow grooves, but are shallower than the narrow grooves.

[0061] As described above, longitudinal shallow grooves 34 are formed in the shoulder land portions 26. The longitudinal shallow grooves 34 extend continuously in the circumferential direction. The longitudinal shallow grooves 34 are included in the circumferential grooves 10. Although not described in detail, the longitudinal shallow grooves 34 have a groove width similar to that of the narrow grooves described above, but are shallower than the narrow grooves. The longitudinal shallow grooves 34 are neither circumferential main grooves 14 nor circumferential narrow grooves 16. The longitudinal shallow grooves 34 intersect with the multiple circumferentially arranged lateral shallow grooves 32. The longitudinal shallow grooves 34 configure the lateral shallow grooves 32 with an inner lateral shallow groove 36 and an outer lateral shallow groove 38. As shown in FIG. 1 , the degree of inclination of the outer lateral shallow groove 38 with respect to the axial direction is gentler than the degree of inclination of the inner lateral shallow groove 36.

[0062] Fig. 3 shows a part of the tread surface 6 shown in Fig. 1. Fig. 3 shows the main land portion 30 located between the equatorial plane and the first end TE1 of the tread surface 6 (i.e., the main land portion 30 located on the first end TE1 side).

[0063] 3, the length indicated by the double-headed arrow WLC is the maximum width of the crown land portion 28 serving as the main land portion 30. In the crown land portion 28 of this tire 2, the ratio (WLC / TW) of the maximum width WLC to the width TW of the tread surface 6 is 17% or more and 27% or less.

[0064] As described above, the multiple circumferential grooves 10 formed in the tread 4 of the tire 2 include one or more circumferential narrow grooves 16. The multiple land portions 24 formed in the tread 4 include one or more main land portions 30. One circumferential narrow groove 16 is formed in each of the one or more main land portions 30. Each of the one or more main land portions 30 includes a circumferential narrow groove 16. As a result, two main narrow land portions 40 are formed in the main land portion 30. The circumferential narrow groove 16 forms two main narrow land portions 40 in the main land portion 30, thereby forming a plurality of main narrow land portions 40 in the tread 4.

[0065] As described above, the tread 4 shown in Fig. 1 has two circumferential narrow grooves 16. Each of the two circumferential narrow grooves 16 is formed in each of the two main land portions 30 formed in the tread 4.

[0066] In Fig. 3, the dashed dotted line LCM is the maximum width center line of the crown land portion 28 serving as the main land portion 30. As shown in Fig. 3, the circumferential narrow groove 16 is located on the maximum width center line LCM of the crown land portion 28. In other words, the circumferential narrow groove 16 is disposed so as to overlap with this maximum width center line LCM in the radial direction.

[0067] In this tire 2, two main narrow land portions 40 are formed in each of two main land portions 30 of the tread 4. In this tread 4, four main narrow land portions 40 are formed between two shoulder land portions 26 and aligned in the axial direction.

[0068] Of the two main narrow land portions 40 that make up the main land portion 30, the main narrow land portion 40 located on the first end TE1 side of the tread surface 6 is called the first main narrow land portion 42, and the main narrow land portion 40 located on the second end TE2 side of the tread surface 6 is called the second main narrow land portion 44. Of the two main narrow land portions 40 that are configured in the main land portion 30, the main narrow land portion 40 located on the equator plane side is called an inner main narrow land portion 46, and the main narrow land portion 40 located on the end TE side of the tread surface 6 is called an outer main narrow land portion 48. In the main land portion 30 located on the first end TE1 side, the first main narrow land portion 42 is the outer main narrow land portion 48, and the second main narrow land portion 44 is the inner main narrow land portion 46. Although not shown, in the main land portion 30 located on the second end TE2 side, the first main narrow land portion 42 is the inner main narrow land portion 46, and the second main narrow land portion 44 is the outer main narrow land portion 48.

[0069] As mentioned above, the tread pattern of the tire 2 includes a plurality of transverse sipes 12 . In the tread 4 shown in Fig. 1, a plurality of transverse sipes 12 are formed at equal intervals in each of four main narrow land portions 40 formed in the tread 4. The interval between two adjacent transverse sipes 12 in one main narrow land portion 40 is the same as the interval between two adjacent transverse sipes 12 in another main narrow land portion 40.

[0070] FIG. 4 shows a cross section of the transverse sipe 12 taken along line IV-IV in FIG. The transverse sipe 12 extends straight in the depth direction thereof. The transverse sipe 12 has a pair of wall surfaces 12W that bridge between the groove mouth 12M and the groove bottom 12T. 4 is the groove width at the groove mouth 12M of the transverse sipe 12. The transverse sipe 12 has a uniform groove width W4 except for a portion of the bottom surface 12B including the groove bottom 12T. The groove width W4 of the transverse sipe 12 is less than 1.0 mm. When a load acts on the tread 4 and the tread 4 is deformed, the wall surfaces 12W of the transverse sipes 12 come into contact with each other and support each other. The length indicated by the double-headed arrow D4 is the groove depth of the transverse sipes 12. The groove depth D4 of the transverse sipes 12 is shallower than the groove depth of the circumferential narrow grooves 16. When the tread 4 wears, the transverse sipes 12 disappear before the circumferential narrow grooves 16.

[0071] In this tire 2, circumferential main grooves 14 and circumferential narrow grooves 16 are arranged alternately in the axial direction between the two shoulder land portions 26. A main narrow land portion 40 is located between the circumferential main groove 14 and the circumferential narrow groove 16. A plurality of transverse sipes 12 formed in the main narrow land portion 40 connect the circumferential main groove 14 and the circumferential narrow groove 16. The transverse sipes 12 cross the main narrow land portion 40.

[0072] In this tire 2, it is sufficient that at least one of the plurality of main narrow land portions 40 formed in the tread 4 has a plurality of transverse sipes 12. Of the four main narrow land portions 40 formed in this tread 4, one main narrow land portion 40 may have a plurality of transverse sipes 12, two main narrow land portions 40 may have a plurality of transverse sipes 12, or three main narrow land portions 40 may have a plurality of transverse sipes 12.

[0073] As described above, the transverse sipes 12 cross the main narrow land portions 40. The transverse sipes 12 function as edge components. From the viewpoint of exhibiting good wet performance, it is preferable that all of the main narrow land portions 40 formed in the tread 4 have a plurality of transverse sipes 12.

[0074] In this tire 2, a plurality of transverse sipes 12 are cut into the main narrow land portion 40, thereby forming a plurality of main blocks 50 in the main narrow land portion 40. The plurality of transverse sipes 12 form a plurality of main blocks 50 in the main narrow land portion 40. The plurality of main blocks 50 are aligned in the circumferential direction.

[0075] 3, the transverse sipes 12 (hereinafter referred to as first transverse sipes 12a) formed in the first main narrow land portion 42 and the transverse sipes 12 (hereinafter referred to as second transverse sipes 12b) formed in the second main narrow land portion 44 are alternately arranged in the circumferential direction. The main blocks 50 (hereinafter referred to as first main blocks 50a) formed in the first main narrow land portion 42 and the main blocks 50 (hereinafter referred to as second main blocks 50b) formed in the second main narrow land portion 44 are alternately arranged in the circumferential direction.

[0076] As described above, the main land portion 30 of the tire 2 includes the circumferential narrow groove 16 . Fig. 5 shows a cross section of the circumferential narrow groove 16 taken along line VV in Fig. 3. Fig. 5 shows a cross section of the circumferential narrow groove 16 taken along a plane perpendicular to the longitudinal direction of the circumferential narrow groove 16. The length indicated by the double-headed arrow D1 in Fig. 5 is the groove depth of the circumferential narrow groove 16. The circumferential narrow groove 16 has a pair of groove walls 16W that bridge between the groove mouth 16M and the groove bottom 16T. In Figure 5, a dashed dotted line CL is the center line of the circumferential narrow groove 16. The circumferential narrow groove 16 has a cross-sectional shape that is symmetrical with respect to the center line CL. The center line CL passes through the groove bottom 16T. The circumferential narrow groove 16 includes a narrow groove portion 52, a widened portion 54, and an inflection portion 56 as geometric elements.

[0077] The narrow groove portion 52 includes the groove opening 16M of the circumferential narrow groove 16. The length indicated by the double-headed arrow W1 in FIG. 5 is the minimum width of the narrow groove portion 52. In the circumferential narrow groove 16 shown in FIG. 5, the narrow groove portion 52 extends straight from the groove opening 16M in the depth direction of the circumferential narrow groove 16. In the cross section of the circumferential narrow groove 16, the outline of the narrow groove portion 52 is represented by a straight line. The narrow groove portion 52 has a uniform groove width W1 as a whole. The minimum width center line of this narrow groove portion 52 coincides with the center line CL mentioned above. The length indicated by the double-headed arrow D2 is the groove depth of the narrow groove portion 52.

[0078] The widened portion 54 is located radially inward of the narrow groove portion 52. The widened portion 54 includes the groove bottom 16T of the circumferential narrow groove 16. The length indicated by the double-headed arrow W2 in FIG. 5 is the maximum width of the widened portion 54. The center line of the maximum width of this widened portion 54 coincides with the center line CL described above. 5, the position indicated by the symbol PM is the position where the widened portion 54 has the maximum width W2 (hereinafter referred to as the maximum width position PM). The portion of the circumferential narrow groove 16 excluding the narrow groove portion 52, i.e., the radially inner portion of the circumferential narrow groove 16, tapers outward from the maximum width position PM and tapers inward from the maximum width position PM. The length indicated by the double-headed arrow D3 is the groove depth from the groove opening 16M of the circumferential narrow groove 16 to the maximum width position PM.

[0079] The length indicated by the double-headed arrow HW2 in Figure 5 is the length from the center line CL to the maximum width position PM. This length HW2 is half the maximum width W2. In the cross section of the circumferential narrow groove 16, the outline of the widened portion 54 is represented by an arc having a radius R2. The length HW2, which is half the maximum width W2, is equal to the radius R2 of the arc representing the outline of the widened portion 54.

[0080] The inflection portion 56 is located between the narrow groove portion 52 and the widened portion 54 in the radial direction. The inflection portion 56 connects the narrow groove portion 52 and the widened portion 54. In the cross section of the circumferential narrow groove 16, the contour of the inflection portion 56 is represented by an arc. In FIG. 5 , arrow R1 indicates the radius of the arc representing the contour of the inflection portion 56.

[0081] 5, the position indicated by the symbol NC is the boundary (hereinafter referred to as the first boundary) between the narrow groove portion 52 and the inflection portion 56. The first boundary NC is the inner end of the narrow groove portion 52 and the outer end of the inflection portion 56. 5, the position indicated by the symbol WC is the boundary (hereinafter referred to as the second boundary) between the widened portion and the inflection portion 56. The second boundary WC is the outer end of the widened portion and the inner end of the inflection portion . Of the circumferential narrow groove 16, the portion from the groove mouth 16M to the first boundary NC is the narrow groove portion 52. The portion from the first boundary NC to the second boundary WC is the inflection portion 56. The portion from the second boundary WC to the groove bottom 16T is the widened portion 54. The straight line representing the outline of the narrow groove portion 52 and the arc representing the outline of the inflection portion 56 are tangent at the first boundary NC. The arc representing the outline of the inflection portion 56 and the arc representing the outline of the widened portion 54 are tangent at the second boundary WC.

[0082] In this tire 2, the maximum width W2 of the widened portion 54 is wider than the minimum width W1 of the narrow groove portion 52. The groove width of the circumferential narrow groove 16 shows the minimum width W1 in the narrow groove portion 52 and shows the maximum width W in the widened portion 54. The circumferential narrow groove 16 is the narrow groove described above.

[0083] A manufacturing method of this tire 2 will be described with reference to Figure 6. In the manufacturing method of this tire 2, elements such as the tread 4 are molded and combined to prepare a raw tire 2r (a tire in an unvulcanized state) for the tire 2. The raw tire 2r is placed in a mold 58. The raw tire 2r is pressurized and heated in the mold 58 to obtain the tire 2. The manufacturing method of this tire 2 includes a step of preparing the raw tire 2r and a step of pressurizing and heating the raw tire 2r in the mold 58. Pressurizing and heating the green tire 2r in the mold 58 is also called vulcanization molding, and the process of pressurizing and heating the green tire 2r is also called a vulcanization process. There are no particular limitations on the vulcanization conditions, such as temperature, pressure, and time, for vulcanizing and molding the green tire 2r in the mold 58, and the vulcanization conditions set for conventional tires are employed. The mold 58 is a general mold for tires.

[0084] Although not described in detail, the mold 58 has a cavity surface 60 on its inner surface. The cavity surface 60 abuts against the outer surface of the green tire 2r and shapes the outer surface of the tire 2. The mold 58 includes a tread ring 62. The tread ring 62 has a tread molding surface 64 on its inner surface. The tread molding surface 64 forms a part of the cavity surface 60. The tread molding surface 64 shapes the tread 4. The mold 58 is a split mold type mold. The tread ring 62 includes a plurality of segments 66 arranged in the circumferential direction. The tread ring 62 is configured by combining these segments 66.

[0085] Although not shown, the segments 66 are movable in the radial direction. After the vulcanization process is completed, the mold 58 is opened to release the tire 2 from the mold 58. At this time, the segments 66 move radially outward. When the green tire 2r is placed in the mold 58, the segments 66 move radially inward. This closes the mold 58, and the vulcanization process begins.

[0086] As described above, the tread 4 of the tire 2 has a tread pattern. This tread pattern is formed on the tread 4 by ridges 68 that reflect the shapes of the grooves 8 that make up the tread pattern. The tread ring 62 has ridges 68 that correspond to the grooves 8. The tread 4 of this tire 2 has circumferential narrow grooves 16. This ridge 68 has narrow ridges 70 that reflect the shape of this circumferential narrow groove 16. The narrow ridges 70 extend continuously in the circumferential direction. The narrow ridges 70 protrude radially inward from a reference surface 64B of the tread molding surface 64. This reference surface 64B of the tread molding surface 64 corresponds to the aforementioned imaginary tread surface.

[0087] The tread pattern of this tire 2 includes, as normal grooves, circumferential main grooves 14, longitudinal shallow grooves 34, and lateral shallow grooves 32 in addition to circumferential narrow grooves 16. Although not shown, the circumferential main grooves 14 are formed by thick convex stripes that reflect the shape of the circumferential main grooves 14. The longitudinal shallow grooves 34 are formed by longitudinal convex stripes that reflect the shape of the circumferential main grooves 14. The lateral shallow grooves 32 are formed by lateral convex stripes that reflect the shape of the circumferential main grooves 14.

[0088] As described above, the shape of the narrow ridge 70 reflects the shape of the circumferential narrow groove 16. The narrow ridge 70 includes a plate portion 72, an intermediate portion 74, and a bulge portion 76. The plate portion 72 corresponds to the narrow groove portion 52 of the circumferential narrow groove 16. The intermediate portion 74 corresponds to the inflection portion 56. The bulge portion 76 corresponds to the widened portion 54. As described above, the circumferential narrow groove 16 has a minimum width W1 at the narrow groove portion 52 and a maximum width W at the widened portion 54. Therefore, the narrow protrusion 70 has a minimum width at the plate portion 72 and a maximum width at the bulged portion 76.

[0089] The tread pattern of this tire 2 includes, as sipes, transverse sipes 12. The transverse sipes 12 are shaped by blades 78. As described above, the transverse sipes 12 connect between the circumferential main grooves 14 and the circumferential narrow grooves 16. The blades 78 connect between the thick ridges (not shown) for the circumferential main grooves 14 and the narrow ridges 70 for the circumferential narrow grooves 16.

[0090] In this method for manufacturing tire 2, once the vulcanization step is completed, tire 2 is released from mold 58. A tire 2 having the tread pattern shown in FIG. 1 is obtained.

[0091] The tread 4 wears with use, causing the grooves 8 to gradually disappear. In the present invention, the stage from a new tire to when the narrow groove portions 52 of the circumferential narrow grooves 16 disappear is the initial stage of wear. The stage from when the narrow groove portions 52 disappear to when the transverse sipes 12 disappear is the intermediate stage of wear. The stage from when the transverse sipes 12 disappear to when the widened portions 54 of the circumferential narrow grooves 16, i.e., the circumferential narrow grooves 16, disappear is the later stage of wear. When the circumferential narrow grooves 16 disappear, it is time to replace the tire 2.

[0092] As described above, the circumferential narrow groove 16 is a narrow groove. In the early stage of wear, the tread 4 comes into contact with the road surface and deforms, causing a pair of groove walls 16W of the circumferential narrow groove 16 to come into contact with each other at the narrow groove portion 52. The main narrow land portions 40 located on both sides of the circumferential narrow groove 16 support each other. When the tread 4 comes into contact with the road surface, deformation of the tread 4 is suppressed. This tire 2 can reduce rolling resistance. The groove volume of the circumferential narrow groove 16 is smaller than the groove volume of the circumferential main groove 14. Compared to a conventional tread in which all of the circumferential grooves 10 located between the two shoulder land portions 26 are configured as circumferential main grooves 14, there is a concern that the wet performance of the tire 2 may be more susceptible to the effects of wear of the tread 4. However, in the early stages of wear, the transverse sipes 12 continue to be exposed even when the tread 4 is worn. Because the transverse sipes 12 can function as edge components, this tire 2 can suppress deterioration of wet performance. The tire 2 can suppress deterioration of wet performance due to wear in the early stage of wear, and can achieve a reduction in rolling resistance.

[0093] In the middle stage of wear, the narrow groove portions 52 disappear, but the volume of the tread 4 decreases. Since deformation of the tread 4 itself is suppressed, the tire 2 can maintain low rolling resistance. Since the transverse sipes 12 continue to be exposed, deterioration of wet performance is suppressed. Even in the middle stage of wear, this tire 2 can suppress deterioration of wet performance due to wear, and can achieve reduced rolling resistance.

[0094] As described above, when the tread 4 wears, the transverse sipes 12 disappear before the circumferential narrow grooves 16. In other words, even if the tread 4 wears and the transverse sipes 12 disappear, the circumferential narrow grooves 16 remain. The circumferential narrow grooves 16 have widened portions 54 on the groove bottom 16T side. In the later stages of wear, the widened portions 54 are exposed. The exposed widened portions 54 can contribute to ensuring groove volume. Even in the later stages of wear, the tire 2 can suppress deterioration in wet performance. In this later stage of wear, the volume of the tread 4 is further reduced. Since the deformation of the tread 4 itself is suppressed, the tire 2 can maintain low rolling resistance. The tire 2 can suppress deterioration of wet performance due to wear even in the later stages of wear, and can achieve a reduction in rolling resistance.

[0095] In the early stage of wear, deformation of the tread 4 is suppressed by the action of the narrow groove portions 52 of the circumferential narrow grooves 16. From the middle stage of wear onwards, deformation of the tread 4 is suppressed by a reduction in the volume of the tread 4. This tire 2 can maintain low rolling resistance from a new state until the tire 2 needs to be replaced. From the early to middle stages of wear, the transverse sipes 12 can function as edge components. In the later stages of wear, the widened portions 54 can contribute to ensuring groove volume. This tire 2 can maintain good wet performance from a new state until the tire 2 needs to be replaced. This tire 2 can suppress deterioration of wet performance due to wear from a new state until the tire 2 needs to be replaced, and can achieve reduction in rolling resistance.

[0096] As described above, in this manufacturing method of the tire 2, once the vulcanization step is completed, the tire 2 is released from the mold 58. At this time, the segments 66 are moved radially outward, and the ridges 68 and the blades 78 are pulled out from the tread 4. The braid 78 bridges between the thick ridges (not shown) and the thin ridges 70. In this mold 58, there are connection portions between the braid 78 and the thick ridges, and connection portions between the braid 78 and the thin ridges 70. The cross-sectional shape of the circumferential main groove 14 tapers inward, for example, as shown in FIG. 2. The thick ridges forming the circumferential main grooves 14 taper toward their tips. This minimizes deformation of the land portions 24 when the thick ridges are pulled out. Furthermore, it is unlikely that a portion of the main narrow land portion will become caught at the connection between the blade 78 and the thick ridge. Pulling out the thick ridges from the tread 4 does not increase stress enough to cause chipping in the tread 4. In contrast, when the thin ridge 70 is pulled out from the tread 4, the bulge 76 passes through the thin groove 52, which has a narrower groove width than the widened portion 54. Pulling out the thin ridge 70 involves deformation of the main land portion 30. Because the width of the bulge 76 is wider than the plate portion 72, a part of the main thin land portion 40 is likely to get caught in the connection between the thin ridge 70 and the blade 78. There is a concern that high stress will be generated in the main thin land portion 40 when the thin ridge 70 is pulled out from the tread 4. Depending on the level of stress generated in the main thin land portion 40, chipping may occur in the main thin land portion 40.

[0097] However, in this tire 2, as described above, the contour of the inflection portion 56 is represented by an arc having a radius R1 in the cross section of the circumferential narrow groove 16 along a plane perpendicular to the longitudinal direction of the circumferential narrow groove 16. The radius R1 of the arc representing the contour of the inflection portion 56 is greater than the length HW2, which is half the maximum width W2 of the widened portion 54.

[0098] In this tire 2, the contour of the portion between the narrow groove portion 52 and the widened portion 54 (i.e., the inflection portion 56) is represented by an arc having a large radius R1. The shape of the inflection portion 56 is configured so that the groove width gradually widens from the narrow groove portion 52 toward the widened portion 54. When the ridges 68 and the blades 78 are pulled out of the tread 4, the main narrow land portion 40 is less likely to get caught at the connection portion between the narrow ridges 70 and the blades 78. Stress concentration at the connection portion between the circumferential narrow groove 16 and the transverse sipe 12 is suppressed. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58 and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance.

[0099] Figure 7 shows a modified example of the cross-sectional shape of the circumferential narrow groove 16 shown in Figure 5. In the circumferential narrow groove 16 shown in Figure 7, the radius R1 of the arc representing the outline of the inflection portion 56 is set smaller than that of the circumferential narrow groove 16 shown in Figure 5, and the maximum width W2 of the widened portion 54 is wider than that of the circumferential narrow groove 16 shown in Figure 5. This circumferential narrow groove 16 has a widened portion 54 with sufficient groove volume. This widened portion 54 can contribute to maintaining good wet performance in the later stages of wear. In this way, by adjusting the radius R1 of the arc that defines the contour of the inflection portion 56 and the maximum width W2 of the widened portion 54, the present invention can provide a circumferential narrow groove 16 that has a cross-sectional shape that is optimal for the specifications of the tire 2 to which the circumferential narrow groove 16 is applied.

[0100] The ratio W1 / W2 of the minimum width W1 of the narrow groove portion 52 to the maximum width W2 of the widened portion 54 is preferably 0.15 or more and 0.35 or less. By setting the ratio W1 / W2 to 0.15 or greater, the main narrow land portion 40 is effectively prevented from getting caught at the connection portion between the narrow convex streak 70 and the blade 78 when the convex streak 68 and the blade 78 are pulled out of the tread 4. Stress concentration at the connection portion between the circumferential narrow groove 16 and the transverse sipe 12 is effectively suppressed. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. From this viewpoint, it is more preferable that the ratio W1 / W2 is 0.20 or greater. By setting the ratio W1 / W2 to 0.35 or less, the widened portions 54 are configured to have the necessary groove volume, so that even if the tread 4 wears and the transverse sipes 12 disappear, the exposed widened portions 54 can contribute to maintaining wet performance. From this perspective, it is more preferable that the ratio W1 / W2 be 0.30 or less.

[0101] The minimum width W1 of the narrow groove portion 52 is preferably 2.5 mm or less. This allows the two main narrow land portions 40 located on both sides of the circumferential narrow groove 16 to support each other, effectively suppressing deformation of the main land portion 30. This tire 2 can reduce rolling resistance. From this perspective, the minimum width W1 is more preferably 2.0 mm or less.

[0102] As described above, in the cross section of the circumferential narrow groove 16 shown in Fig. 5, the outline of the widened portion is represented by an arc having a radius R2. In this case, the ratio R1 / R2 of the radius R1 of the arc representing the outline of the inflection portion 56 to the radius R2 of the arc representing the outline of the widened portion 54 is preferably 1.5 or greater. This suppresses an increase in stress generated in the inflection portion 56 when the ridge 68 and the blade 78 are pulled out of the tread 4. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. From this viewpoint, the ratio R1 / R2 is more preferably 2.0 or greater.

[0103] The ratio D2 / D1 of the groove depth D2 of the narrow groove portion 52 to the groove depth D1 of the circumferential narrow groove 16 is preferably 0.25 or more and 0.70 or less. By setting the ratio D2 / D1 to be 0.25 or greater, the narrow groove portion 52 can contribute to suppressing deformation of the main land portion 30. This tire 2 can reduce rolling resistance. From this viewpoint, it is more preferable that the ratio D2 / D1 be 0.30 or greater. By setting the ratio D2 / D1 to 0.70 or less, the contour of the inflection portion 56 of the tire 2 can be expressed by an arc having a large radius R1. This suppresses an increase in stress that occurs at the inflection portion 56 when the ridge 68 and the blade 78 are pulled out of the tread 4. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. From this viewpoint, it is more preferable that the ratio D2 / D1 be 0.65 or less.

[0104] As shown in FIG. 5 , the groove depth D4 of the transverse sipes 12 is deeper than the groove depth D2 of the narrow groove portions 52. This allows the transverse sipes 12 to function as edge components from the initial to intermediate stages of wear. This tire 2 can maintain good wet performance. The groove depth D4 of the transverse sipes 12 is shallower than the groove depth D3 from the groove opening 16M of the circumferential narrow groove 16 to the position PM where the widened portion 54 has the maximum width W2. This reduces the impact of the transverse sipes 12 on the rigidity of the tread 4. The narrow groove portions 52 can effectively contribute to suppressing deformation of the main land portion 30. This tire 2 can reduce rolling resistance. Furthermore, the length of the connecting portion between the circumferential narrow groove 16 and the transverse sipes 12 is set to an appropriate length. When the ridges 68 and the blades 78 are pulled out of the tread 4, the main narrow land portion 40 is effectively prevented from getting caught at the connecting portion between the narrow ridges 70 and the blades 78. This effectively suppresses stress concentration at the connection portion between the circumferential narrow groove 16 and the transverse sipe 12. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. The tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58 and the deterioration of wet performance due to wear, thereby achieving a reduction in rolling resistance. From this viewpoint, it is preferable that the groove depth D3 from the groove mouth 16M of the circumferential narrow groove 16 to the position PM where the widened portion 54 has the maximum width W2, the groove depth D4 of the transverse sipe 12, and the groove depth D2 of the narrow groove portion 52 satisfy the following formula. Formula: D2≦D4≦D3

[0105] When the groove depth D3 from the groove mouth 16M of the circumferential narrow groove 16 to the position PM where the widened portion 54 shows the maximum width W2, the groove depth D4 of the transverse sipes 12, and the groove depth D2 of the narrow groove portions 52 satisfy the above formula, from the viewpoint of being able to suppress the occurrence of tread chipping when the tire 2 is released from the mold 58 and the deterioration of wet performance due to wear, and achieving a reduction in rolling resistance, it is more preferable that the ratio D2 / D4 of the groove depth D2 of the narrow groove portions 52 to the groove depth D4 of the transverse sipes 12 be 0.40 or more and 0.90 or less, and that the ratio D3 / D4 of the groove depth D3 from the groove mouth 16M of the circumferential narrow groove 16 to the position PM where the widened portion 54 shows the maximum width W2 to the groove depth D4 of the transverse sipes 12 be 1.05 or more and 2.00 or less.

[0106] In FIG. 3, angle θ is the angle that the transverse sipe 12 makes with respect to the axial direction. The angle θ is preferably equal to or greater than -35 degrees and equal to or less than 35 degrees. In this case, stress concentration at the corners of the main blocks 50, i.e., the portions where the transverse sipes 12 join the circumferential narrow grooves 16, is suppressed. The tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. From this viewpoint, the angle θ is more preferably equal to or greater than -25 degrees and equal to or less than 25 degrees.

[0107] The tread pattern of this tire 2 has a plurality of pitch patterns 80 arranged in the circumferential direction. In other words, the tread pattern is formed by combining a plurality of pitch patterns 80. In this specification, a pitch pattern means a unit pattern that is repeated in the circumferential direction of the tire.

[0108] In Figure 1, the two-dot chain line PL extending in the axial direction is the boundary between two adjacent pitch patterns 80. In the present invention, the boundary PL is defined as a line extending straight in the axial direction without intersecting with grooves other than the circumferential grooves 10. The pattern located between the two adjacent boundaries is the pitch pattern 80, and all of the pitch patterns 80 constituting the tread pattern have the same pattern.

[0109] 1, the length indicated by the double-headed arrow L is the circumferential length of the pitch pattern 80. All of the pitch patterns 80 constituting the tread pattern have the same circumferential length L. The length indicated by the double-headed arrow L1 is the distance between two transverse sipes 12 arranged side by side in the circumferential direction.

[0110] In the tire 2, the ratio L / L1 of the circumferential length L of the pitch pattern 80 to the interval L1 between two circumferentially aligned transverse sipes 12 is preferably 1.0 or greater and 3.5 or less. By setting the ratio L / L1 to 1.0 or greater, the transverse sipes 12 can effectively function as edge components, and the tire 2 can maintain good wet performance. From this viewpoint, the ratio L / L1 is more preferably 1.5 or greater. By setting the ratio L / L1 to 3.5 or less, the effect of the transverse sipes 12 on the rigidity of the tread 4 is suppressed, and the narrow groove portion 52 can effectively contribute to suppressing deformation of the main land portion 30. This tire 2 can reduce rolling resistance. An appropriate number of connection portions between the circumferential narrow grooves 16 and the transverse sipes 12 are configured. This tire 2 can suppress the occurrence of tread chipping when the tire 2 is released from the mold 58. From this viewpoint, it is more preferable that the ratio L / L1 is 3.0 or less.

[0111] For example, as shown in FIG. 3, the circumferential narrow groove 16 extends in a meandering manner in the circumferential direction. The circumferential narrow groove 16 includes a first longitudinal narrow groove 82 near the first end TE1 of the tread surface 6, a second longitudinal narrow groove 84 near the second end TE2, and a connecting narrow groove 86 connecting the first longitudinal narrow groove 82 and the second longitudinal narrow groove 84. Among the connecting narrow grooves 86, the connecting narrow groove 86 that connects the first longitudinal narrow groove 82 located on the first circumferential direction side and the second longitudinal narrow groove 84 located on the second circumferential direction side is also referred to as a first connecting narrow groove 86a. The connecting narrow groove 86 that connects the second longitudinal narrow groove 84 located on the first circumferential direction side and the first longitudinal narrow groove 82 located on the second circumferential direction side is also referred to as a second connecting narrow groove 86b. When a groove unit is formed by connecting the first longitudinal narrow groove 82, the first connecting narrow groove 86a, the second longitudinal narrow groove 84, and the second connecting narrow groove 86b in this order, the circumferential narrow groove 16 is formed by connecting a plurality of such groove units in the circumferential direction. The first longitudinal narrow grooves 82 and the second longitudinal narrow grooves 84 are arranged alternately in the circumferential direction.

[0112] In the circumferential narrow grooves 16 arranged between the equatorial plane and the first end TE1 of the tread surface 6, the first longitudinal narrow groove 82 located on the axially outer side is also called the outer longitudinal narrow groove 88, and the second longitudinal narrow groove 84 located on the axially inner side is also called the inner longitudinal narrow groove 90. Although not shown, in the circumferential narrow grooves 16 arranged between the equatorial plane and the second end TE2 of the tread surface 6, the first longitudinal narrow groove 82 is arranged axially inward, and the second longitudinal narrow groove 84 is arranged axially outward. The second longitudinal narrow groove 84 located axially outward is also called an outer longitudinal narrow groove 88, and the first longitudinal narrow groove 82 located axially inward is also called an inner longitudinal narrow groove 90.

[0113] As described above, when the tread 4 comes into contact with the road surface and deforms, the groove walls 16W of the circumferential narrow grooves 16 come into contact with each other at the narrow groove portions 52. Here, the circumferential narrow grooves 16 do not extend circumferentially in a straight line but extend circumferentially in a meandering manner, so the groove walls 16W effectively mesh with each other. The main narrow land portions 40 located on both sides of the circumferential narrow groove 16 constrain each other. Deformation of the main land portion 30 is effectively suppressed. The tire 2 can further reduce rolling resistance. From this perspective, the circumferential narrow groove 16 includes a first longitudinal narrow groove 82 near the first end TE1 of the tread surface 6, a second longitudinal narrow groove 84 near the second end TE2, and a connecting narrow groove 86 connecting the first longitudinal narrow groove 82 and the second longitudinal narrow groove 84, and it is preferable that the first longitudinal narrow grooves 82 and the second longitudinal narrow grooves 84 are arranged alternately in the circumferential direction.

[0114] As shown in FIG. 3 , the first transverse sipe 12 a of the first main narrow land portion 42 merges into the second longitudinal narrow groove 84 near the second end TE2 of the tread surface 6, and the second transverse sipe 12 b of the second main narrow land portion 44 merges into the first longitudinal narrow groove 82 near the first end TE1 of the tread surface 6. In the main land portion 30, the first transverse sipes 12a and the second transverse sipes 12b are arranged without any gap between them. Compared to when the first transverse sipes 12a and the second transverse sipes 12b are arranged with a gap between them, the first transverse sipes 12a and the second transverse sipes 12b can function more effectively as edge components. This tire 2 has good wet performance. From this perspective, it is preferable that the first transverse sipes 12a of the first main narrow land portion 42 merge into the second longitudinal narrow groove 84 near the second end TE2 of the tread surface 6, and the second transverse sipes 12b of the second main narrow land portion 44 merge into the first longitudinal narrow groove 82 near the first end TE1 of the tread surface 6.

[0115] As described above, the crown circumferential main groove 20 is located on the equatorial plane. For example, as shown in FIG. 3, the crown circumferential main groove 20 does not extend straight in the circumferential direction, but rather extends in a zigzag pattern in the circumferential direction. Specifically, the crown circumferential main groove 20 includes a first apex 20ETa close to a first end TE1 of the tread surface 6 and a second apex 20ETb close to a second end TE2 (not shown) of the tread surface 6. The crown circumferential main groove 20 extends in a zigzag pattern, alternately passing through the first apex 20ETa and the second apex 20ETb in the circumferential direction. The crown circumferential main groove 20 can function as an edge component from a new state until the tire 2 needs to be replaced. The crown circumferential main groove 20 can contribute to suppressing deterioration of wet performance due to wear. From this viewpoint, it is preferable that the crown circumferential main groove 20 includes a first apex 20ETa close to a first end TE1 of the tread surface 6 and a second apex 20ETb close to a second end TE2 of the tread surface 6, and extends in a zigzag pattern while alternately passing through the first apex 20ETa and the second apex 20ETb in the circumferential direction.

[0116] 3 , for example, the first apex 20ETa of the crown circumferential main groove 20 overlaps in the axial direction with the outer longitudinal narrow groove 88 of the circumferential narrow groove 16 located on the first end TE1 side of the tread surface 6 of the crown circumferential main groove 20. Although not shown, the second apex 20ETb of the crown circumferential main groove 20 overlaps in the axial direction with the outer longitudinal narrow groove 88 of the circumferential narrow groove 16 located on the second end TE2 side of the tread surface 6 of the crown circumferential main groove 20. The first apex 20ETa and the second apex 20ETb of the crown circumferential main groove 20 each overlap in the axial direction with the outer longitudinal narrow groove 88 of the circumferential narrow groove 16 located adjacent to the crown circumferential main groove 20. In this tire 2, even though the crown circumferential main groove 20 extends in a zigzag pattern in the circumferential direction, the difference between the maximum width and the minimum width of the inner main narrow land portion 46 located between the crown circumferential main groove 20 and the circumferential narrow groove 16 can be made small. Changes in the contact state between the tread 4 and the road surface while the tire 2 makes one rotation are suppressed. In this tire 2, the occurrence of uneven wear is suppressed. The circumferential narrow groove 16 and the transverse sipes 12 can stably perform their functions from a new state until the tire 2 needs to be replaced. This tire 2 can maintain good wet performance and low rolling resistance from a new state until the tire 2 needs to be replaced. From this viewpoint, when the crown circumferential main groove 20 includes a first apex 20ETa close to the first end TE1 of the tread surface 6 and a second apex 20ETb close to the second end TE2 of the tread surface 6, and extends in a zigzag manner while alternately passing through the first apex 20ETa and the second apex 20ETb in the circumferential direction, it is more preferable that each of the first apex 20ETa and the second apex 20ETb of the crown circumferential main groove 20 overlaps in the axial direction with the outer longitudinal narrow groove 88 of the circumferential narrow groove 16 located adjacent to this crown circumferential main groove 20. In this case, from the viewpoint of ensuring the rigidity of the corners of the main blocks 50 formed at the portions where the transverse sipes 12 join the crown circumferential main grooves 20 of the tire 2 and effectively suppressing the occurrence of tread chipping, it is more preferable that the transverse sipes 12 joining the outer longitudinal narrow grooves 88 join the crown circumferential main grooves 20 at the first apex 20ETa and the second apex 20ETb of the crown circumferential main grooves 20 that overlap with the outer longitudinal narrow grooves 88 in the axial direction.

[0117] Fig. 8 shows another modified example of the circumferential narrow groove 16. In the circumferential narrow groove 16 shown in Fig. 8, the groove opening 16M is tapered. The narrow groove portion 52 of this circumferential narrow groove 16 includes a tapered portion 92 and a narrow groove body 94. This circumferential narrow groove 16 has the same configuration as the circumferential narrow groove 16 shown in FIG. 5, except that the narrow groove portion 52 is composed of a tapered portion 92 and a narrow groove body 94 .

[0118] The tapered portion 92 includes the groove opening 16M of the circumferential narrow groove 16. The tapered portion 92 tapers inward from the groove opening 16M. The outline of the tapered portion 92 shown in FIG. 6 is represented by a straight line. This outline may also be represented by a curved line. The length indicated by the double-headed arrow D5 is the groove depth of the tapered portion 92. The narrow groove body 94 is located radially inside the tapered portion 92. The narrow groove body 94 is continuous with the tapered portion 92. The narrow groove body 94 extends straight in the depth direction of the circumferential narrow groove 16. The contour of the narrow groove body 94 is represented by a straight line. In this circumferential narrow groove 16, when the tread 4 comes into contact with the road surface and deforms, a pair of groove walls 16W of the circumferential narrow groove 16 come into contact with each other at the narrow groove body 94 of the narrow groove portion 52.

[0119] 8, the position indicated by the symbol PU is the boundary between the tapered portion 92 and the narrow groove main body 94. The boundary PU is represented by the intersection of the contour line of the tapered portion 92 and the contour line of the narrow groove main body 94. As shown in FIG. 8, when the boundary between the tapered portion 92 and the narrow groove main body 94 is rounded, the boundary PU is represented by the intersection of the extension line of the contour line of the tapered portion 92 and the extension line of the contour line of the narrow groove main body 94.

[0120] From the viewpoint that the tire 2 can effectively suppress the concentration of strain at the groove openings 16M of the circumferential narrow grooves 16 while ensuring the groove volume of the circumferential narrow grooves 16, it is preferable that the ratio (D5 / D1) of the groove depth D5 of the tapered portion 92 to the groove depth D1 of the circumferential narrow grooves 16 is 0.12 or more and 0.14 or less.

[0121] As is clear from the above explanation, according to the present invention, a heavy-duty tire 2 can be obtained that can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve reduced rolling resistance. [Industrial Applicability]

[0122] The technology described above, which can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve reduced rolling resistance, can be applied to various tires.

[0123] [Note] The present invention includes the following aspects.

[0124] [1] A tire having a tread that comes into contact with the road surface; The tread has a tread pattern including a plurality of circumferential grooves extending continuously in the circumferential direction and a plurality of transverse sipes arranged in the circumferential direction, the plurality of circumferential grooves include a plurality of circumferential main grooves and one or more circumferential narrow grooves, Each of the plurality of circumferential main grooves has a pair of groove walls that do not come into contact with the road surface even when the tread comes into contact with the road surface and deforms, The plurality of circumferential main grooves define a plurality of land portions aligned in the axial direction in the tread, The plurality of land portions include two shoulder land portions located at the outermost sides in the axial direction and one or more main land portions located between the two shoulder land portions, One or more of the main land portions each include the circumferential narrow groove, The circumferential narrow groove forms two main narrow land portions in the main land portion, thereby forming a plurality of main narrow land portions in the tread, At least one of the plurality of main narrow land portions has a plurality of the transverse sipes, and the plurality of the transverse sipes connect between the circumferential main groove and the circumferential narrow groove, the circumferential narrow groove includes a narrow groove portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and an inflection portion connecting the narrow groove portion and the widened portion, When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other at the narrow groove portion, The maximum width W2 of the widened portion is wider than the minimum width W1 of the narrow groove portion, In a cross section of the circumferential narrow groove along a plane perpendicular to the longitudinal direction of the circumferential narrow groove, the contour of the inflection portion is represented by an arc having a radius R1, The radius R1 is greater than half the length HW2 of the maximum width W2 of the widened portion. Heavy duty tires. [2] The heavy-duty tire according to the above-mentioned [1], wherein the ratio W1 / W2 of the minimum width W1 of the narrow groove portion to the maximum width W2 of the widened portion is 0.15 or more and 0.35 or less. [3] The heavy-duty tire according to the above [1] or [2], wherein the narrow groove portion has a minimum width W1 of 2.5 mm or less. [4] In a cross section of the circumferential narrow groove along a plane perpendicular to the longitudinal direction of the circumferential narrow groove, the outline of the widened portion is represented by an arc having a radius R2, The heavy-duty tire according to any one of the above-mentioned [1] to [3], wherein the ratio R1 / R2 of the radius R1 of the arc representing the outline of the inflection portion to the radius R2 of the arc representing the outline of the widened portion is 1.5 or more. [5] A heavy-duty tire according to any one of the above [1] to [4], wherein the ratio D2 / D1 of the groove depth D2 of the narrow groove portion to the groove depth D1 of the circumferential narrow groove is 0.25 or more and 0.70 or less. [6] A heavy-duty tire according to any one of the above [1] to [5], wherein a groove depth D3 from the groove mouth of the circumferential narrow groove to a position where the widened portion has a maximum width W2, a groove depth D4 of the transverse sipe, and a groove depth D2 of the narrow groove portion satisfy the following formula: Formula: D2≦D4≦D3 [7] The heavy-duty tire according to any one of [1] to [6] above, wherein the angle formed by the transverse sipes with respect to the axial direction is equal to or greater than -35 degrees and equal to or less than 35 degrees. [8] The tread pattern has a plurality of pitch patterns arranged in a circumferential direction and having the same circumferential length, The plurality of pitch patterns have the same pattern,

[0023] The heavy-duty tire according to any one of the above-mentioned [1] to [7], wherein a ratio L / L1 of a circumferential length L of the pitch pattern to a spacing L1 between two circumferentially arranged transverse sipes is 1.0 or more and 3.5 or less. [Explanation of symbols]

[0125] 2. Tires 4. Tread 6. Tread surface 8...Groove 10...Circumferential groove 12. Transverse sipes 14, 18, 20... Circumferential main groove 16... Circumferential narrow groove 24, 26, 28... Rikubu 30 Main Land Area 40 Main land area 52...Narrow groove part 54 Widened section 56...inflection section 58···Mold 60...cavity surface 62 Tread ring 64 Tread molding surface 66 segments 68···Convex strip 70... Thin convex strips 72 Plate section 74 Middle section 76...bulge 78···Blade 80 pitch pattern

Claims

1. It has a tread that comes into contact with the road surface, The tread has a tread pattern including a plurality of circumferential grooves extending continuously in the circumferential direction and a plurality of transverse sipes arranged in the circumferential direction, the plurality of circumferential grooves include a plurality of circumferential main grooves and one or more circumferential narrow grooves, Each of the plurality of circumferential main grooves has a pair of groove walls that do not come into contact with the road surface even when the tread comes into contact with the road surface and deforms, The plurality of circumferential main grooves define a plurality of land portions arranged in the axial direction in the tread, the plurality of land portions include two shoulder land portions located axially outermost and one or more main land portions located between the two shoulder land portions, One or more of the main land portions each include the circumferential narrow groove, The circumferential narrow groove forms two main narrow land portions in the main land portion, thereby forming a plurality of main narrow land portions in the tread, At least one of the plurality of main narrow land portions has a plurality of the transverse sipes, and the plurality of the transverse sipes connect between the circumferential main groove and the circumferential narrow groove, the circumferential narrow groove includes a narrow groove portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and an inflection portion connecting the narrow groove portion and the widened portion, When the tread comes into contact with the road surface and deforms, a pair of groove walls of the circumferential narrow groove come into contact with each other at the narrow groove portion, The maximum width W2 of the widened portion is wider than the minimum width W1 of the narrow groove portion, In a cross section of the circumferential narrow groove along a plane perpendicular to the longitudinal direction of the circumferential narrow groove, the contour of the inflection portion is represented by an arc having a radius R1, The radius R1 is greater than a length HW2 that is half the maximum width W2 of the widened portion. Heavy duty tires.

2. a ratio W1 / W2 of the minimum width W1 of the narrow groove portion to the maximum width W2 of the widened portion is 0.15 or more and 0.35 or less; 2. The heavy duty tire according to claim 1.

3. The minimum width W1 of the narrow groove portion is 2.5 mm or less.

2. The heavy duty tire according to claim 1.

4. In a cross section of the circumferential narrow groove along a plane perpendicular to the length direction of the circumferential narrow groove, a contour of the widened portion is represented by an arc having a radius R2, a ratio R1 / R2 of a radius R1 of the arc representing the contour of the inflection portion to a radius R2 of the arc representing the contour of the widened portion is 1.5 or more; 2. The heavy duty tire according to claim 1.

5. a ratio D2 / D1 of a groove depth D2 of the narrow groove portion to a groove depth D1 of the circumferential narrow groove is 0.25 or more and 0.70 or less; 2. The heavy duty tire according to claim 1.

6. A groove depth D3 from the groove opening of the circumferential narrow groove to a position where the widened portion has a maximum width W2, a groove depth D4 of the transverse sipe, and a groove depth D2 of the narrow groove portion satisfy the following formula:

2. The heavy duty tire according to claim 1. Formula: D2≦D4≦D3

7. The angle formed by the transverse sipe with respect to the axial direction is greater than or equal to -35 degrees and less than or equal to 35 degrees.

2. The heavy duty tire according to claim 1.

8. The tread pattern includes a plurality of pitch patterns arranged in a circumferential direction and having the same circumferential length, The plurality of pitch patterns have the same pattern, A ratio L / L1 of a circumferential length L of the pitch pattern to a spacing L1 between two transverse sipes arranged in the circumferential direction is 1.0 or more and 3.5 or less.

2. The heavy duty tire according to claim 1.

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