Tire for heavy load and manufacturing method of tire for heavy load

Abstract

To provide a tire 2 for heavy load which can restrain tread chip from generating when released from a mold 104 and can restrain wet performance from deteriorating due to abrasion wear and can reduce rolling resistance.SOLUTION: A tire 2 is provided with a tread 4. The tread 4 comprises a plurality of circumferential grooves 10 and a plurality of lateral direction sipes 74. The plurality of circumferential grooves 10 contains a circumferential narrow groove 18. The circumferential narrow groove 18 comprises a narrow groove part 62, a widening part 56 and a first inflection part 58. When the tread 4 comes into contact with road surface and then deforms, a pair of wall surfaces 18w of the circumferential narrow groove 18 comes into contact with each other in the narrow groove part 62. The lateral direction sipes 74 connect to the circumferential narrow groove 18. The lateral direction sipes 74 comprise a sipe body 76, a tubular part 78 and a second inflection part 80. Contour of the second inflection part 80 is represented by a circular arc which includes radius RL1. Radius RC1 of the circular arc which represents the contour of the first inflection part 58 is larger than half of maximum width WC2 of the widening part 56.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heavy duty tire and a method for manufacturing a heavy duty tire. [Background technology]

[0002] The tread of a tire is where it comes into contact with the road surface, and the tread pattern, which is made up of grooves carved into the tread, affects the tire's performance. The tread pattern has a plurality of circumferential grooves that define a plurality of land portions in the tread. The tread deforms when it comes into contact with the road surface. Tread deformation affects the rolling resistance of the tire. 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 tread deformation. 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 reduce rolling resistance. [Means for solving the problem]

[0008] The heavy-duty tire according to the present invention has a tread whose tread surface contacts the road surface. The tread has a tread pattern including a plurality of circumferential grooves and a plurality of lateral sipes. The plurality of circumferential grooves form a plurality of land portions in the tread. The plurality of land portions include a pair of outer land portions located axially outermost and including the edges of the tread surface, and a plurality of inner land portions located between the pair of outer land portions and aligned in the axial direction. The plurality of circumferential grooves include a circumferential main groove located between each of the outer land portions and the inner land portion located axially inside the outer land portion, and a circumferential narrow groove located between two adjacent inner land portions. The circumferential narrow groove includes a body portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and a first inflection portion connecting the body portion and the widened portion. The body portion includes a narrow groove portion. The maximum width WC2 of the widened portion is wider than the minimum width WC1 of the narrow groove portion. When the tread comes into contact with the road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other at the narrow groove portion. In a cross section of the circumferential narrow groove, the outline of the first inflection portion is represented by an arc having a radius RC1. At least one of the inner land portions includes the lateral sipe. The lateral sipe is connected to the circumferential narrow groove. The lateral sipe includes a sipe body including the groove mouth of the lateral sipe, a tubular portion including the groove bottom of the lateral sipe, and a second inflection portion connecting the sipe body and the tubular portion. The maximum width WL2 of the tubular portion is wider than the minimum width WL1 of the sipe body. In a cross section of the lateral sipe, the outline of the second inflection portion is represented by an arc having a radius RL1. The radius RC1 of the arc representing the outline of the first inflection portion is greater than half the maximum width WC2 of the widened portion.

[0009] A heavy-duty tire manufacturing method according to the present invention is the above-described heavy-duty tire manufacturing method. This manufacturing method includes a step of pressurizing and heating a green tire for the tire in a mold. The mold includes a tread ring that forms the tread. The tread ring includes a pattern forming portion that forms the tread pattern. The pattern forming portion includes main groove ridges that form the circumferential main grooves, narrow groove ridges that form the circumferential narrow grooves, and lateral blades that form the lateral sipes. The tread ring includes a plurality of dividing surfaces that cross the pattern forming portion. The plurality of dividing surfaces divide the tread ring into a plurality of segments that are arranged circumferentially. The plurality of segments are movable in the radial direction of the tire. In each of the segments, the lateral blade closest to the dividing surface forms an angle of 15 degrees or less with respect to the direction of movement of the segment. [Effects of the Invention]

[0010] The present invention can 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 reduce rolling resistance. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a development view showing a portion of a tread of a heavy duty tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a development view showing a part of FIG. [Figure 3] FIG. 2 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2. [Figure 5] FIG. 10 is a cross-sectional view showing a modified example of the circumferential narrow groove. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] 1 is a cross-sectional view showing a part of a vulcanizer used in a method for manufacturing a heavy-duty tire according to one embodiment of the present invention. [Figure 8]FIG. 10 is a plan view illustrating opening and closing of a mold. [Figure 9] FIG. 2 is a development view showing a part of the pattern forming section. [Figure 10] FIG. 10 is a cross-sectional view taken along line XX in FIG. 9. [Figure 11] FIG. 10 is a cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 3 is a cross-sectional view showing a part of a cross section taken along line XII-XII in FIG. 2. [Figure 13] 10 is a cross-sectional view showing the relationship between the protruding direction of the horizontal blade and the moving direction of the segment. FIG. [Figure 14] FIG. 10 is a plan view showing the relationship between the pitch pattern and the division surface. [Figure 15] FIG. 10 is a development view showing a modified example of the dividing surface. [Figure 16] FIG. 10 is a cross-sectional view showing a modified example of a horizontal blade. [Figure 17] FIG. 10 is a cross-sectional view showing a modified example of a lateral sipe. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0013] 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.

[0014] In the present invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] [Findings that form the basis of the present invention] As mentioned above, providing narrow circumferential grooves in the tread suppresses deformation of the tread when it comes into contact with the road surface. 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. For example, sipes that extend across the land area (hereafter referred to as lateral sipes) can function as edge components. By providing lateral sipes in the land area, the tire can suppress a decline in wet performance.

[0021] The tread wears, which reduces the volume of the grooves cut into the tread. This reduction in groove volume leads to a decrease in drainage performance. By providing circumferential narrow grooves and lateral sipes in the tread, tires can reduce rolling resistance while suppressing a decrease in wet performance in the early stages of wear. However, there is concern that the groove volume will decrease and wet performance will decrease from the middle stage of wear onwards. Therefore, in order to suppress the deterioration of wet performance after the middle stage of wear, it is being considered to provide a widened portion on the groove bottom side of the circumferential narrow groove and a tubular portion on the groove bottom side of the lateral sipe.

[0022] When circumferential narrow grooves or lateral sipes are cut into the tread, the tread ring of the mold is provided with ridges that reflect the shape of the circumferential narrow grooves or blades that reflect the shape of the lateral sipes. When widened portions are provided in the circumferential narrow grooves to suppress deterioration of wet performance, the shape of the widened portions is reflected in the tip portions of the convex stripes. When the vulcanization process is completed and the tire is released from the mold, the tip of the ridge passes through the narrow groove, which is narrower than the widened section. The pulling out of the ridge involves deformation of the land section. For example, when a lateral sipe is provided across a land portion sandwiched between two circumferential narrow grooves, the blade for the lateral sipe is connected to the ridge for the circumferential narrow groove. This mold has a connection portion between the ridge and the blade (hereinafter referred to as the ridge-blade connection portion). Since a bulge is formed at the tip of the ridge, when the tire is released from the mold, the rubber tends to get caught on the ridge blade connection part. When the mold is a split mold, the closer to the circumferential end of the segment, the more the ridges and blades are pulled out at an angle to their protruding direction. When the ridge-blade connection portion is located at the circumferential end of the segment, the stress acting on the land portion is concentrated in the portion in contact with this connection portion, and depending on the degree of stress, there is a concern that chipping may occur in the land portion (i.e., the tread). If a tubular portion is provided on the groove bottom side of the lateral sipes in order to suppress the deterioration of wet performance after the middle stage of wear, it is expected that the risk of tread chipping will further increase.

[0023] Therefore, the inventors have conducted extensive research into the shapes of the circumferential narrow grooves and lateral sipes 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 that can reduce rolling resistance, and have completed the present invention, which will be described below.

[0024] [Outline of the embodiment of the present invention] The present invention relates to a tire tread having a tread surface that comes into contact with a road surface, the tread having a tread pattern including a plurality of circumferential grooves and a plurality of lateral sipes, the plurality of circumferential grooves constituting a plurality of land portions in the tread, the plurality of land portions including a pair of outer land portions located axially outermost and including an edge of the tread surface, and a plurality of inner land portions located between the pair of outer land portions and aligned in the axial direction, the plurality of circumferential grooves including a circumferential main groove located between each of the outer land portions and the inner land portion located axially inside the outer land portion, and a circumferential narrow groove located between two adjacent inner land portions, the circumferential narrow groove having a body portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and a first inflection portion connecting the body portion and the widened portion, the body portion having a narrow groove portion, and a maximum width WC2 of the widened portion being equal to or smaller than the minimum width WC1 of the narrow groove portion. a width WC1 of the circumferential narrow groove that is wider than a width WC1 of the tread; when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other at the narrow groove portion; an outline of the first inflection portion in a cross section of the circumferential narrow groove is represented by an arc having a radius RC1; at least one of the inner land portions has the lateral sipe, the lateral sipe is connected to the circumferential narrow groove, the lateral sipe comprises a sipe body including a groove mouth of the lateral sipe, a tubular portion including a groove bottom of the lateral sipe, and a second inflection portion connecting the sipe body and the tubular portion; a maximum width WL2 of the tubular portion is wider than a minimum width WL1 of the sipe body;

[0025] 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 reduce rolling resistance. The mechanism by which the tire exhibits these effects has not been clarified, but is presumed to be as follows.

[0026] In the tire of the present invention, when the tread comes into contact with the road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other at the narrow groove portion. The two inner land portions arranged on either side of the circumferential narrow groove support each other, suppressing deformation of the inner land portions. This tire can reduce rolling resistance. The lateral sipe body can function as an edge component, allowing the tire to maintain good wet performance even as the tread wears. The maximum width WC2 of the widened portion is wider than the minimum width WC1 of the narrow groove portion, and the maximum width WL2 of the tubular portion is wider than the minimum width WL1 of the sipe body. The widened portions of the circumferential narrow grooves and the tubular portions of the lateral sipes contribute to ensuring groove volume. Even if the tread wears and the sipe body disappears, the exposed tubular portions and widened portions can contribute 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 reduce rolling resistance.

[0027] As will be described later, the mold for this tire includes narrow groove ridges that form circumferential narrow grooves and lateral blades that form lateral sipes. After the vulcanization process is completed, the tire is released from the mold. At this time, the narrow groove ridges and lateral blades are pulled out from the tread.

[0028] In this tire, the contour of the first inflection portion of the circumferential narrow groove and the contour of the second inflection portion of the lateral sipe are expressed by a single circular arc. The first inflection portion and the second inflection portion are configured with smooth shapes. Despite the circumferential narrow groove having a widened portion and the lateral sipe having a tubular portion, the resistance force when pulling the narrow groove ridge and lateral blade out of the tread is reduced. In particular, because the radius RC1 of the circular arc that expresses the contour of the first inflection portion is greater than half the maximum width WC2 of the widened portion, the resistance force when pulling the narrow groove ridge out of the tread is effectively reduced, and the rubber is prevented from getting caught at the ridge blade connection portion. This tire can also reduce the occurrence of tread chipping when released from the mold. This tire can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, thereby reducing rolling resistance.

[0029] Preferably, the radius RL1 of the arc defining the contour of the second inflection portion is greater than half the maximum width WL2 of the tubular portion. In this case, the resistance force when the blade is pulled out of the tread is effectively reduced. This tire can reduce the occurrence of tread chipping when released from the mold.

[0030] Preferably, the ratio WC1 / WC2 of the minimum width WC1 of the narrow groove portion to the maximum width WC2 of the widened portion is 0.10 or greater and 0.35 or less. In this case, the tire can be prevented from having chipped treads when released from the mold and from having poor wet performance due to wear.

[0031] Preferably, the narrow groove portion has a minimum width WC1 of 2.5 mm or less, in which case the tire can reduce rolling resistance.

[0032] Preferably, a ratio D2 / D1 of a groove depth D2 of the body portion of the circumferential narrow groove to a groove depth D1 of the circumferential narrow groove is 0.25 or more and 0.70 or less. In this case, the tire can be prevented from having tread chipping when released from the mold, and the rolling resistance can be reduced.

[0033] Preferably, the groove depth D2 of the body portion of the circumferential narrow groove, the groove depth D3 from the groove mouth of the circumferential narrow groove to the position where the widened portion shows the maximum width WC2, and the groove depth D5 of the lateral sipe satisfy the following formula. Formula:D2 <D5<D3 In this case, the tire can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, thereby reducing rolling resistance.

[0034] The present invention is a method for manufacturing the heavy-duty tire described above, comprising a step of pressurizing and heating a green tire for the tire in a mold, wherein the mold has a tread ring that forms the tread, the tread ring has a pattern forming portion that forms the tread pattern, the pattern forming portion has main groove ridges that form the circumferential main grooves, narrow groove ridges that form the circumferential narrow grooves, and lateral blades that form the lateral sipes, the tread ring has a plurality of dividing surfaces that cross the pattern forming portion, the plurality of dividing surfaces divide the tread ring into a plurality of segments that are aligned in the circumferential direction, the plurality of segments are movable in the radial direction of the tire, and in each of the segments, the lateral blade closest to the dividing surface forms an angle of 15 degrees or less with respect to the moving direction of the segment.

[0035] In conventional molds, the number of segments constituting a tread ring, i.e., the number of divisions of the tread ring, is set to 8 to 10. When the number of divisions of the tread ring is set to the same as in conventional molds, the angle that the lateral blade closest to the dividing surface makes with respect to the moving direction of the segments is 18.0 to 22.5 degrees. In contrast, in the manufacturing method of the present invention, the angle that the lateral blade closest to the dividing surface makes with respect to the moving direction of the segments is 15 degrees or less. This manufacturing method can reduce the deviation between the protruding direction of the lateral blade and the moving direction of the segments. This manufacturing method can prevent rubber from getting caught at the connecting portion of the blade ridges. Stress concentration occurring near the connecting portion of the blade ridges is reduced. This manufacturing method can prevent tread chipping and blade damage when releasing the tire.

[0036] Preferably, the number of segments included in the tread ring is 17 or more. In this case, the mold used in this manufacturing method can set the angle of the lateral blade closest to the dividing surface relative to the moving direction of the segments to 10.6 degrees or less. This mold can further reduce the deviation between the protruding direction and the withdrawing direction of the lateral blade. This manufacturing method can suppress the occurrence of tread chipping and blade damage when releasing the tire.

[0037] Preferably, the radius RC1 of the arc defining the contour of the first inflection portion is greater than the shortest distance from the lateral blade closest to the parting surface to the parting surface, in which case the mold can suppress the occurrence of tread chipping when the tire is released.

[0038] Preferably, in a development view of the pattern forming portion, the outline of the dividing surface includes at least one arc. In this case, the mold can suppress the occurrence of tread chipping when the tire is released.

[0039] Preferably, the lateral sipe formed by the lateral blade closest to the parting surface has a cross-sectional shape asymmetric with respect to the minimum width centerline of the sipe body, the lateral sipe has an outer groove wall formed by a first side surface of the lateral blade facing the parting surface, and an inner groove wall formed by a second side surface of the lateral blade located opposite the first side surface, and the maximum width centerline of the tubular portion is located closer to the outer groove wall than the minimum width centerline of the sipe body. In this case, this mold can suppress the occurrence of tread chipping when the tire is released.

[0040] As described above, the present invention provides a heavy-duty tire that can suppress the occurrence of tread chipping during release from the mold and the deterioration of wet performance due to wear, thereby reducing rolling resistance. This will be explained in detail below using the heavy-duty tire shown in Figure 1 as an example.

[0041] [Details of the embodiment of the present invention] [tire] 1 is a plan view showing a part 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.

[0042] 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 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. A dashed line EL extending in the circumferential direction represents the equatorial plane of the tire 2. The direction from the equatorial plane toward the edge of the tread surface, which will be described later, is the outer side in the axial direction of the tire 2, and the direction from the edge of the tread surface toward the equatorial plane is the inner side in the axial direction of the tire 2. The direction indicated by arrow CD1 is the first circumferential direction side of the tire 2, and the direction indicated by arrow CD2 is the second circumferential direction side of the tire 2. The tread 4 of this tire 2 comes into contact with the road surface from the first circumferential direction side toward the second circumferential direction side. The first circumferential direction side is the leading side of the tire 2, and the second circumferential direction side is the trailing side of the tire 2.

[0043] The tire 2 has a tread 4. The tread 4 is made of crosslinked rubber. 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 includes a tread surface 6. The tire 2 comes into contact with the road surface at the tread surface 6. The tread 4 has the tread surface 6 that comes into contact with the road surface.

[0044] The tread 4 is one of the elements that make up the tire 2. The tire 2 includes, as its parts, a tread portion that comes into contact with the road surface, a pair of sidewall portions, and a pair of bead portions. The tread 4 is included in the tread portion.

[0045] In the present invention, there is no particular limitation on the internal structure of the tire 2. Although not described in detail, the tire 2 has a general internal structure as an internal structure of a heavy-duty tire. The tread 4 is an element that constitutes this internal structure.

[0046] Grooves 8 are cut into the tread 4. This forms a tread pattern. The tread 4 has a tread pattern. 1 shows a tread pattern configured on a tread 4. Using this tread pattern as an example, an overview of the tread pattern that is the subject of the present invention will be explained. The tread pattern in FIG. 1 is that of a new tire 2, that is, an unworn tread 4. FIG. 2 shows a portion of the tread pattern shown in FIG.

[0047] The intersection of the tread surface 6 and the equatorial plane is the equator. When the groove 8 is located on the equatorial plane, the equator is identified based on a virtual outer surface obtained assuming that the groove 8 does not exist.

[0048] The solid line (or position) indicated by the symbol TE represents the edge of the tread surface 6 . In a tire, if the edge of the tread surface 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 contacting the tire with a flat surface is used as the edge of the tread surface.

[0049] In the tread surface 6 shown in Figure 1, one end TE of the tread surface 6 located on the left side of the equatorial plane is called a first end TE1. The other end TE located on the right side of the equatorial plane is called a second end TE2. The end TE on the left side of the equatorial plane may be called the second end TE2, and the end TE on the right side of the equatorial plane may be called the first end TE1.

[0050] 1 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.

[0051] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1. Fig. 3 shows a cross-section of a groove 8, more specifically, a shoulder circumferential groove, which will be described later. The main configuration of the groove 8 will be described based on Fig. 3. 3, 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.

[0052] The groove 8 has a pair of groove walls 8W that bridge between the groove mouth 8M and the groove bottom 8T. In the groove 8, the portion including the groove bottom 8T is also called the bottom surface 8B. In this case, the portion of the groove wall 8W other than the bottom surface 8B, i.e., the portion between the bottom surface 8B and the groove mouth 8M, is also called the wall surface 8S. The groove 8 has a pair of wall surfaces 8S including a groove mouth 8M, and a bottom surface 8B including a groove bottom 8T. The groove width of the groove 8 is represented by the shortest distance between a pair of wall surfaces 8S, that is, a first wall surface 8S and a second wall surface 8S (hereinafter referred to as the wall-to-wall distance). The wall-to-wall distance is measured along a plane including a pair of edges 8E that form the groove opening 8M, or along a plane parallel to this plane.

[0053] The length indicated by the double-headed arrow WG in Figure 3 is the groove width of the groove 8 at the groove mouth 8M. The groove width WG is measured along a plane including 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 a plane including 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.

[0054] The groove bottom 8T is the deepest position in the cross section of the groove 8. The distance from this plane including the left and right edges 8E that make up the groove mouth 8M to the bottom surface 8B is measured along the normal to this plane. The position where the distance from this plane to the bottom surface 8B is greatest is the groove bottom 8T. The direction of the normal to the plane including the left and right edges 8E is the depth direction of the groove 8.

[0055] 3 is a curved surface. This bottom surface 8B may be configured as a flat surface. In this case, the width center of the flat surface configuring the bottom surface 8B is used as the groove bottom 8T. If a protrusion is provided on the bottom surface 8B, the groove bottom 8T is identified based on a virtual bottom surface obtained assuming that the protrusion does not exist.

[0056] A groove 8 having a groove width WG of less than 1.0 mm at its groove mouth 8M is also 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. Ordinary grooves with a narrow groove width that allows a pair of wall surfaces to come into contact with each other when the tread comes into contact with the road surface and deforms are also called narrow grooves, while ordinary grooves with a wide groove width that prevents a pair of wall surfaces from coming into contact with each other when the tread comes into contact with the road surface and deforms are also called main grooves.

[0057] A plurality of circumferential grooves 10 are cut into the tread 4 of this tire 2 and aligned in the axial direction. Each circumferential groove 10 extends continuously in the circumferential direction. The tread 4 has a plurality of circumferential grooves 10 that are aligned in the axial direction and extend continuously in the circumferential direction.

[0058] 3, the length indicated by the double-headed arrow DGs is the groove depth of the circumferential groove 10, specifically, the shoulder circumferential groove described later. The groove depth DGs of the shoulder circumferential groove 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 DGs is preferably 13 mm or more and 18 mm or less.

[0059] In the present invention, of the multiple circumferential grooves cut in the tread, the circumferential groove located at the outermost position in the axial direction is the shoulder circumferential groove. The circumferential groove located on the equatorial plane is the center circumferential groove. When no circumferential groove is provided on the equatorial plane, the circumferential groove closest to the equatorial plane is the center circumferential groove. When a circumferential groove is located between the center circumferential groove and the shoulder circumferential groove, this circumferential groove is the middle circumferential groove.

[0060] The tread 4 of this tire 2 has four circumferential grooves 10. Of the four circumferential grooves 10, the circumferential groove 10 located at the outermost position in the axial direction is a shoulder circumferential groove 12. The circumferential groove 10 closest to the equatorial plane is a center circumferential groove 14. This tread 4 has a pair of center circumferential grooves 14 and a pair of shoulder circumferential grooves 12.

[0061] Of the pair of center circumferential grooves 14, the center circumferential groove 14 located on the first end TE1 side of the tread surface 6 is also called the first center circumferential groove 14a, and the center circumferential groove 14 located on the second end TE2 side is also called the second center circumferential groove 14b. Of the pair of shoulder circumferential grooves 12, the shoulder circumferential groove 12 located on the first end TE1 side of the tread surface 6 is also called the first shoulder circumferential groove 12a, and the shoulder circumferential groove 12 located on the second end TE2 side is also called the second shoulder circumferential groove 12b.

[0062] The shoulder circumferential grooves 12 of this tire 2 have a groove width that prevents a pair of wall surfaces 12S from contacting each other even when the tread 4 comes into contact with the road surface and deforms. The shoulder circumferential grooves 12 are the aforementioned main grooves and are also called circumferential main grooves 16. As will be described later, the center circumferential groove 14 has a groove width that causes a pair of wall surfaces to contact each other in the narrow groove portion when the tread 4 comes into contact with the road surface and deforms. The center circumferential groove 14 is the aforementioned narrow groove and is also called circumferential narrow groove 18. The plurality of circumferential grooves 10 include a circumferential main groove 16 and a circumferential narrow groove 18 .

[0063] The tread 4 of this tire 2 has two shoulder circumferential grooves 12 arranged on either side of the equatorial plane, i.e., a first shoulder circumferential groove 12a and a second shoulder circumferential groove 12b. The first shoulder circumferential groove 12a is also referred to as a first circumferential main groove 16a, and the second shoulder circumferential groove 12b is also referred to as a second circumferential main groove 16b. The tread 4 further has two center circumferential grooves 14 arranged on either side of the equatorial plane, namely, a first center circumferential groove 14a and a second center circumferential groove 14b. The first center circumferential groove 14a is also called a first circumferential narrow groove 18a, and the second center circumferential groove 14b is also called a second circumferential narrow groove 18b.

[0064] 1, the length indicated by the double arrow WGc is the groove width at the groove opening of the center circumferential groove 14. The length indicated by the double arrow WGs is the groove width at the groove opening of the shoulder circumferential groove 12. The ratio (WGc / TW) of the groove width WGc of the center circumferential groove 14 to the width TW of the tread surface 6 is 2.0% or less. As shown in FIG. 1 , the groove width WGs of the shoulder circumferential groove 12 is wider than the groove width WGc of the center circumferential groove 14. The ratio (WGs / TW) of the groove width WGs of the shoulder circumferential groove 12 to the width TW of the tread surface 6 exceeds 2.0%. Specifically, the ratio (WGs / TW) is preferably 4.0% or more and 10% or less.

[0065] The shoulder circumferential groove 12, i.e., the circumferential main groove 16, of this tire 2 includes an outer apex 12s close to the edge TE of the tread surface 6 and an inner apex 12u close to the equatorial plane. The outer apexes 12s and the inner apexes 12u are arranged alternately in the circumferential direction. The circumferential main groove 16 extends circumferentially, alternately passing through the outer apexes 12s and the inner apexes 12u. The circumferential main groove 16 extends in a zigzag manner in the circumferential direction. The circumferential main groove 16 may also extend straight in the circumferential direction.

[0066] The center circumferential groove 14 of the tire 2 extends in a meandering manner in the circumferential direction. The center circumferential groove 14 may also extend in a straight manner in the circumferential direction.

[0067] The central circumferential groove 14 of this tire 2 includes a first narrow groove 44 near a first end TE1 of the tread surface 6, a second narrow groove 46 near a second end TE2 of the tread surface 6, and a connecting narrow groove 48 connecting the first narrow groove 44 and the second narrow groove 46. Of the connecting narrow grooves 48, the connecting narrow groove 48 that connects the first narrow groove 44 and the second narrow groove 46 located on the rear side of the first narrow groove 44 is also called a first connecting narrow groove 48a. The connecting narrow groove 48 that connects the second narrow groove 46 and the first narrow groove 44 located on the rear side of the second narrow groove 46 is also called a second connecting narrow groove 48b. When a groove unit is formed by connecting the first narrow groove 44, the first connecting narrow groove 48a, the second narrow groove 46, and the second connecting narrow groove 48b in this order, the center circumferential groove 14 is formed by connecting a plurality of such groove units in the circumferential direction. The first narrow grooves 44 and the second narrow grooves 46 are arranged alternately in the circumferential direction.

[0068] The first narrow groove 44 and the second narrow groove 46 of the center circumferential groove 14 extend straight in the circumferential direction. The first narrow groove 44 and the second narrow groove 46 have a constant length in the circumferential direction. The first narrow groove 44 of the second center circumferential groove 14b has the same length as the second narrow groove 46 of the first center circumferential groove 14a. The second narrow groove 46 of the second center circumferential groove 14b has the same length as the first narrow groove 44 of the first center circumferential groove 14a. The first narrow groove 44 of the first center circumferential groove 14a and the second narrow groove 46 of the second center circumferential groove 14b are located on the end TE side of the tread surface 6. The second narrow groove 46 of the first center circumferential groove 14a and the first narrow groove 44 of the second center circumferential groove 14b are located on the equator plane side. For ease of explanation, the first narrow groove 44 of the first center circumferential groove 14a and the second narrow groove 46 of the second center circumferential groove 14b will be referred to as outer narrow grooves 50, and the second narrow groove 46 of the first center circumferential groove 14a and the first narrow groove 44 of the second center circumferential groove 14b will be referred to as inner narrow grooves 52. The first connecting narrow groove 48a of the first center circumferential groove 14a and the second connecting narrow groove 48b of the second center circumferential groove 14b will be referred to as outer connecting grooves 48s. The outer connecting groove 48s connects the outer narrow groove 50 to the inner narrow groove 52 located on the rear side of the outer narrow groove 50. The second connecting narrow groove 48b of the first center circumferential groove 14a and the first connecting narrow groove 48a of the second center circumferential groove 14b will be referred to as inner connecting grooves 48u. The inner connecting groove 48u connects the inner narrow groove 52 to the outer narrow groove 50 located on the rear side of the inner narrow groove 52. Each of the first central circumferential groove 14a and the second central circumferential groove 14b, i.e., each of the first circumferential narrow groove 18a and the second circumferential narrow groove 18b, includes an outer narrow groove 50 near the edge of the tread surface 6, an inner narrow groove 52 near the equatorial plane, an outer connecting groove 48s connecting the outer narrow groove 50 and the inner narrow groove 52 located on the trailing side of the outer narrow groove 50, and an inner connecting groove 48u connecting the inner narrow groove 52 and the outer narrow groove 50 located on the trailing side of the inner narrow groove 52. The outer narrow grooves 50 and the inner narrow grooves 52 are arranged alternately in the circumferential direction.

[0069] As described above, the tread 4 has a plurality of circumferential grooves 10. The plurality of circumferential grooves 10 form a plurality of land portions 20 in the tread 4.

[0070] In the present invention, among the multiple land portions configured in the tread, the land portion located outermost in the axial direction is the shoulder land portion. The land portion located on the equatorial plane is the center land portion. If no land portion is provided on the equatorial plane, the land portion closest to the equatorial plane is the center land portion. If a land portion is located between the center land portion and the shoulder land portion, this land portion is the middle land portion.

[0071] The tread 4 of this tire 2 has five land portions 20. Of the five land portions 20, the land portion 20 located axially outermost is a shoulder land portion 22. The shoulder land portion 22 includes an edge TE of the tread surface 6. The land portion 20 located on the equatorial plane is a center land portion 24. The land portion 20 located between the center land portion 24 and the shoulder land portion 22 is a middle land portion 26. This tread 4 has a center land portion 24, a pair of middle land portions 26, and a pair of shoulder land portions 22. Of the pair of middle land portions 26, the middle land portion 26 located on the first end TE1 side of the tread surface 6 is also called the first middle land portion 26a, and the middle land portion 26 located on the second end TE2 side is also called the second middle land portion 26b. Of the pair of shoulder land portions 22, the shoulder land portion 22 located on the first end TE1 side of the tread surface 6 is also called the first shoulder land portion 22a, and the shoulder land portion 22 located on the second end TE2 side is also called the second shoulder land portion 22b. Although not described in detail, the width of each land portion 20 is determined appropriately according to the specifications of the tire 2.

[0072] In the present invention, among the plurality of land portions, the land portion located axially outermost and including the edge of the tread surface is also referred to as an outer land portion. The plurality of land portions includes a pair of outer land portions. The land portion located between the pair of outer land portions is also referred to as an inner land portion.

[0073] The tread 4 shown in FIG. 1 has a center land portion 24, a pair of middle land portions 26, and a pair of shoulder land portions 22. Of these land portions 20, the two shoulder land portions 22 located axially outermost and including the edge TE of the tread surface 6 are outer land portions 28. The center land portion 24 and the pair of middle land portions 26 located between the pair of shoulder land portions 22 are inner land portions 30. The center land portion 24 is also referred to as an inner center land portion 30c. Each of the pair of middle land portions 26 is also referred to as an inner middle land portion 30m. Of the pair of middle land portions 26, the first middle land portion 26a is also referred to as a first inner middle land portion 30m1, and the second middle land portion 26b is also referred to as a second inner middle land portion 30m2. The multiple land portions 20 configured in this tread 4 include a pair of outer land portions 28 located axially outermost and including the edge TE of the tread surface 6, and multiple inner land portions 30 located between the pair of outer land portions 28 and aligned in the axial direction. In this tire 2, at least two inner land portions 30 are provided between the pair of outer land portions 28. The tread 4 shown in FIG. 1 has three inner land portions 30.

[0074] On each of the first end TE1 side and the second end TE2 side of the tread surface 6, between the shoulder land portion 22 and the middle land portion 26 is a shoulder circumferential groove 12. As described above, the shoulder circumferential groove 12 is a circumferential main groove 16. The circumferential main groove 16 is located between an outer land portion 28 and an inner land portion 30 located axially inward of the outer land portion 28. Between the middle land portion 26 and the center land portion 24 is the center circumferential groove 14. As described above, the center circumferential groove is the circumferential narrow groove 18. The circumferential narrow groove 18 is located between two adjacent inner land portions 30.

[0075] In this tire 2, a plurality of lateral grooves 32 that cross the land portions 20 are cut into all of the land portions 20 that are formed in the tread 4. As a result, a plurality of blocks 34 that are aligned in the circumferential direction are formed in each land portion 20. In the tread 4 of this tire 2, a plurality of land portions 20 are aligned in the axial direction, and each land portion 20 has a plurality of blocks 34 that are aligned in the circumferential direction. The tread pattern of this tire 2 is a block pattern. Although not described in detail, the lateral grooves 32 are normal grooves. The lateral grooves 32 are shallower than the circumferential grooves 10.

[0076] The lateral grooves 32 formed in the inner center land portion 30c bridge between the inner narrow grooves 52 of the first circumferential narrow grooves 18a and the inner narrow grooves 52 of the second circumferential narrow grooves 18b. The lateral grooves 32 formed in the inner middle land portion 30m bridge between the inner apexes 12u of the circumferential main grooves 16 and the outer narrow grooves 50 of the circumferential narrow grooves 18. The lateral grooves 32 formed in the outer land portion 28 bridge between the outer apexes 12s of the circumferential main grooves 16 and the edge TE of the tread surface 6.

[0077] Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 2. Fig. 4 shows a cross section of the center circumferential groove 14, that is, the circumferential narrow groove 18. The circumferential narrow groove 18 has a pair of groove walls 18W connecting the groove mouth 18M and the groove bottom 18T. In the circumferential narrow groove 18, the portion including the groove bottom 18T is also referred to as a bottom surface 18B. In this case, the portion of the groove wall 18W other than the bottom surface 18B, i.e., the portion between the bottom surface 18B and the groove mouth 18M, is also referred to as a wall surface 18S. The circumferential narrow groove 18 has a pair of wall surfaces 18S including the groove mouth 18M and the bottom surface 18B including the groove bottom 18T. A dashed line LC is the center line of the circumferential narrow groove 18. The circumferential narrow groove 18 has a cross-sectional shape that is symmetrical with respect to the center line LC. The center line LC extends in the depth direction of the circumferential narrow groove 18 and passes through the groove bottom 18T.

[0078] The circumferential narrow groove 18 includes a body portion 54, a widened portion 56, and a first inflection portion 58. The body portion 54 includes a groove mouth 18M of the circumferential narrow groove 18. The widened portion 56 includes a groove bottom 18T of the circumferential narrow groove 18. The first inflection portion 58 is located between the body portion 54 and the widened portion 56 in the radial direction. When the tread 4 wears and the body portion 54 disappears, the first inflection portion 58 is exposed. When the first inflection portion 58 disappears, the widened portion 56 is exposed.

[0079] The body portion 54 of this tire 2 includes a funnel portion 60 and a narrow groove portion 62. The groove opening 18M of this circumferential narrow groove 18 is tapered. As shown in Fig. 5, the body portion 54 may be configured only with the narrow groove portion 62 without providing the funnel portion 60.

[0080] The funnel portion 60 includes the groove mouth 18M of the circumferential narrow groove 18. The funnel portion 60 tapers inward from the groove mouth 18M. 4, the length indicated by the double arrow WA is the groove width at the groove mouth 18M of the funnel portion 60. The groove width WA of the funnel portion 60 is preferably 0.15 to 0.45 times the groove width WGs of the shoulder circumferential groove 12, i.e., the circumferential main groove 16.

[0081] The funnel portion 60 includes an inclined portion 64 and a connecting portion 66. The inclined portion 64 includes the groove opening 18M of the circumferential narrow groove 18. The groove width of the inclined portion 64 gradually decreases from the groove opening 18M toward the connecting portion 66. In the cross section of the circumferential narrow groove 18 shown in FIG. 4, the outline of the inclined portion 64 is represented by a straight line. The position indicated by the symbol H1 is the radially inner end of the inclined portion 64. The connecting portion 66 connects the inclined portion 64 and the narrow groove portion 62. The radially inner end H1 of the inclined portion 64 is also the radially outer end of the connecting portion 66. Position H1 is the boundary between the inclined portion 64 and the connecting portion 66. The groove width of the connecting portion 66 gradually decreases from the radial outer end H1 toward the narrow groove portion 62. In the cross section of the circumferential narrow groove 18 shown in FIG. 4, the outline of the connecting portion 66 is represented by an arc. Arrow Rb indicates the radius of the arc representing the outline of the connecting portion 66. This arc representing the outline of the connecting portion 66 is tangent to the straight line representing the outline of the inclined portion 64 at the boundary H1. In the cross section of the circumferential narrow groove shown in Figure 4, the portion represented by the arc of radius Rb is also called the upper arc portion 68. The position indicated by the symbol H2 is the radially inner end of this upper arc portion 68. The aforementioned boundary H1 is also the radially outer end of this upper arc portion 68.

[0082] The narrow groove portion 62 is located radially inside the funnel portion 60. The narrow groove portion 62 is continuous with the funnel portion 60. The length indicated by the double arrow WC1 in Figure 4 is the minimum width of the narrow groove portion 62. The center line of the minimum width of the narrow groove portion 62 coincides with the center line LC described above. The minimum width WC1 of the narrow groove portion 62 is set so that a pair of wall surfaces 18S of the circumferential narrow groove 18 come into contact with each other at the narrow groove portion 62 when the tread 4 comes into contact with the road surface and deforms.

[0083] The narrow groove portion 62 extends in the depth direction of the circumferential narrow groove 18. The narrow groove portion 62 shown in FIG. 4 has a portion that extends straight in the depth direction (hereinafter also referred to as a straight portion 70). The straight portion 70 is a portion of the narrow groove portion 62 that has a uniform groove width WC1 in the depth direction. The narrow groove portion 62 includes the straight portion 70 that has a uniform groove width WC1 in the depth direction. Although not shown, the narrow groove portion 62 may be configured so that the groove width gradually increases from the position showing the minimum width WC1 toward the funnel portion 60 and the first inflection portion 58, for example.

[0084] As described above, when the groove opening 8M of the groove 8 is tapered, the groove width at the groove opening 8M of the groove 8 is expressed based on the virtual edge obtained assuming that the groove is not tapered. The groove width WGc at the groove opening 18M of the circumferential narrow groove 18 shown in FIG. 4 is expressed as the minimum width WC1 of the narrow groove portion 62.

[0085] In the cross section of the circumferential narrow groove 18, the outline of the straight portion 70 is represented by a straight line. The radially inner end H2 of the upper arc portion 68 described above is also the radially outer end of the straight portion 70. Position H2 is the boundary between the upper arc portion 68 and the straight portion 70. The straight line representing the outline of the straight portion 70 is tangent to the arc representing the outline of the upper arc portion 68 at the boundary H2. The position indicated by symbol H3 in FIG. 4 is the radially inner end of this straight portion 70.

[0086] The widened portion 56 is located radially inward of the body portion 54. The widened portion 56 includes the groove bottom 18T of the circumferential narrow groove 18. The widened portion 56 has a rounded contour. The widened portion 56 is curved so as to bulge outward from its inner side. 4, the length indicated by the double-headed arrow WC2 is the maximum width of the widened portion 56. The center line of the widened portion 56 coincides with the center line LC described above.

[0087] The position indicated by the symbol PX is the position where the widened portion 56 has the maximum width WC2 (hereinafter referred to as the maximum width position). The portion of the circumferential narrow groove 18 excluding the body portion 54, in other words, the radially inner portion of the circumferential narrow groove 18, tapers outward from the maximum width position PX and tapers inward from the maximum width position PX.

[0088] The widened portion 56 of the tire 2 is represented by a single arc having a radius Rw in the outline of the cross section of the circumferential narrow groove 18 shown in Figure 4. The center of the arc representing the outline of the widened portion 56 is located on the center line LC. The radius Rw of the arc representing the outline of the widened portion 56 is equal to half the length of the maximum width WC2 of the widened portion 56.

[0089] The first inflection portion 58 connects the narrow groove portion 62 and the widened portion 56. The groove width of the first inflection portion 58 gradually increases from the narrow groove portion 62 toward the widened portion 56. The first inflection portion 58 curves so as to recess inward from its outer side. Specifically, in the cross section of the circumferential narrow groove 18, the outline of the first inflection portion 58 is represented by a circular arc. In FIG. 4, arrow RC1 indicates the radius of the arc representing the outline of the first inflection portion 58. In the cross section of the circumferential narrow groove shown in FIG. 4 , the portion represented by the arc of radius RC1 is also referred to as the first boundary arc portion 72. The radially inner end H3 of the straight portion 70 described above is the radially outer end of the first boundary arc portion 72. Position H3 is the boundary between the straight portion 70 and the first boundary arc portion 72. The arc representing the outline of the first boundary arc portion 72 is tangent to the straight line representing the outline of the straight portion 70 at the boundary H3. The position indicated by symbol H4 is the radially inner end of the first boundary arc portion 72. The radially inner end H4 is the radially inner end of the first inflection portion 58 and is the boundary with the widened portion 56.

[0090] 4, the position indicated by the solid line LTP is the boundary between the funnel portion 60 and the narrow groove portion 62. This boundary LTP is represented by the position at the boundary between the funnel portion 60 and the narrow groove portion 62 where the circumferential narrow groove 18 exhibits a width Wa that is 1.1 times the minimum width WC1 of the narrow groove portion 62. When the portion exhibiting the width Wa that is 1.1 times the minimum width WC1 has a certain length, the radially inner end of that portion is used as the boundary LTP. The position indicated by the solid line LPE is the boundary between the narrow groove portion 62 and the first inflection portion 58, in other words, the boundary between the trunk portion 54 and the first inflection portion 58. This boundary LPE is represented by the position at the boundary between the trunk portion 54 and the first inflection portion 58 where the circumferential narrow groove 18 exhibits a width Wb that is 1.1 times the minimum width WC1 of the narrow groove portion 62. When the portion exhibiting the width Wb that is 1.1 times the minimum width WC1 has a certain length, the radially outer end of that portion is used as the boundary LTP.

[0091] In FIG. 4, the length indicated by the double-headed arrow D1 is the groove depth of the circumferential narrow groove 18. The length indicated by the double-headed arrow D2 is the groove depth of the body portion 54 of the circumferential narrow groove 18. The groove depth D2 is represented by the depthwise distance from the groove opening 18M of the circumferential narrow groove 18 to the boundary LPE between the body portion 54 and the first inflection portion 58. The length indicated by the double-headed arrow D3 is the groove depth from the groove opening 18M of the circumferential narrow groove 18 to the position PX where the widened portion 56 has the maximum width WC2. This groove depth D3 is also called the maximum width groove depth. The length indicated by the double-headed arrow D4 is the groove depth of the funnel portion 60. The groove depth D4 is represented by the depthwise distance from the groove opening 18M of the circumferential narrow groove 18 to the boundary LTP between the funnel portion 60 and the narrow groove portion 62.

[0092] The groove depth D1 of the circumferential narrow groove 18 of this tire 2 is the same as the groove depth DGs of the shoulder circumferential groove 12, or the circumferential narrow groove 18 is shallower than the shoulder circumferential groove 12. Specifically, the ratio D1 / DGs of the groove depth D1 of the circumferential narrow groove 18 to the groove depth DGs of the shoulder circumferential groove 12 is 0.75 or more and 1.00 or less.

[0093] As described above, the tread 4 of this tire 2 is configured with a plurality of land portions 20 aligned in the axial direction. Of the plurality of land portions 20, each block 34 (hereinafter, referred to as inner block 34u) configured in the inner land portion 30 located between a pair of outer land portions 28 is provided with a lateral sipe 74. In other words, the inner land portion 30 is provided with the lateral sipe 74. Each inner land portion 30 includes a plurality of inner blocks 34u aligned in the circumferential direction. Each inner land portion 30 includes a plurality of lateral sipes 74 aligned in the circumferential direction.

[0094] The tread 4 of this tire 2 has three inner land portions 30. As shown in Fig. 2, each of the three inner land portions 30 has a lateral sipe 74. In this tire 2, it is sufficient that at least one of the multiple inner land portions 30 provided in the tread 4 has the lateral sipe 74. Only the center inner land portion 30c may have the lateral sipe 74, or only the pair of middle inner land portions 30m may have the lateral sipe 74.

[0095] In the tire 2, the inner-center land portion 30c and the pair of inner-middle land portions 30m are provided with lateral sipes 74. The lateral sipes 74 (hereinafter, center lateral sipes 74c) formed in the blocks of the inner-center land portion 30c (hereinafter, center inner blocks 34uc) bridge between the outer narrow grooves 50 of the first circumferential narrow groove 18a and the outer narrow grooves 50 of the second circumferential narrow groove 18b. The lateral sipes 74 (hereinafter, middle lateral sipes 74m) formed in the blocks of the inner-middle land portion 30m (middle inner blocks 34um) bridge between the vicinity of the inner apex 12u of the circumferential main groove 16 and the inner narrow groove 52 of the circumferential narrow groove 18. The middle lateral sipes 74m and the center lateral sipes 74c provided in this tire 2 are connected to the circumferential narrow groove 18. In other words, the lateral sipes 74 of this tire 2 are connected to the circumferential narrow groove 18.

[0096] The lateral sipes 74 provided in each inner block 34u bridge between two circumferential grooves 10 arranged on either side of the inner block 34u. The lateral sipes 74 are transverse sipes that cross the inner block 34u. One end of the lateral sipe 74 may remain within the inner block 34u, and the other end of the lateral sipe 74 may be connected to one circumferential groove 10. In this case, the lateral sipe 74 is connected to one circumferential groove 10.

[0097] FIG. 6 shows a cross section of the lateral sipe 74 taken along line VI-YI in FIG. 2. The cross section of the lateral sipe 74 shown in FIG. 6 is a cross section of the center lateral sipe 74c. As described above, the lateral sipes 74 are also provided in the middle inner block 34um. The cross-sectional shape of the lateral sipe 74 in the middle inner block 34um, i.e., the middle lateral sipe 74m, is the same as the cross-sectional shape of the center lateral sipe 74c. The cross-sectional shape of the lateral sipe 74 will be described based on the center lateral sipe 74c, and a description of the cross-sectional shape of the middle lateral sipe 74m will be omitted.

[0098] The lateral sipes 74 have a pair of groove walls 74W connecting the groove mouth 74M and the groove bottom 74T. In the lateral sipes 74, the portion including the groove bottom 74T is also referred to as a bottom surface 74B. In this case, the portion of the groove wall 74W other than the bottom surface 74B, i.e., the portion between the bottom surface 74B and the groove mouth 74M, is also referred to as a wall surface 74S. The lateral sipes 74 have a pair of wall surfaces 74S including the groove mouth 74M and a bottom surface 74B including the groove bottom 74T. The dashed dotted line LY is the center line of the lateral sipe 74. The lateral sipe 74 has a cross-sectional shape that is symmetrical with respect to the center line LY. The center line LY extends in the depth direction of the lateral sipe 74 and passes through the groove bottom 74T.

[0099] The lateral sipes 74 include a sipe body 76, a tubular portion 78, and a second inflection portion 80. The sipe body 76 includes the groove mouth 74M of the lateral sipe 74. The tubular portion 78 includes the groove bottom 74T of the lateral sipe 74. The second inflection portion 80 is located radially between the sipe body 76 and the tubular portion 78. When the tread 4 wears and the sipe body 76 disappears, the second inflection portion 80 is exposed. When the second inflection portion 80 disappears, the tubular portion 78 is exposed.

[0100] The sipe body 76 extends in the depth direction from the groove opening 74M. The length indicated by the double arrow WL1 in Figure 6 is the minimum width of the sipe body 76. The minimum width center line of the sipe body 76 coincides with the above-mentioned center line LY.

[0101] The sipe body 76 is the sipe described above. The groove width of the sipe body 76 is less than 1.0 mm. Therefore, the minimum width WL1 is also less than 1.0 mm. As described above, the sipe body 76 includes the groove opening 74M of the lateral sipe 74. The groove width Wp at the groove opening 74M of the lateral sipe 74 is less than 1.0 mm. 6, the solid line LM is the boundary line between the sipe body 76 and the second inflection portion 80. The length indicated by the double-headed arrow WM is the groove width of the lateral sipe 74 measured along this boundary line LM. The boundary line LM is set at a position where the groove width WM is 1.0 mm. The groove width of the portion outside the boundary line LM, i.e., the sipe main body 76, is less than 1.0 mm. The groove width of the portion inside this boundary line LM, i.e., the second inflection portion 80 and the tubular portion 78, is 1.0 mm or more. The groove width of the second inflection portion 80 and the tubular portion 78 is wider than the groove width of the sipe main body 76.

[0102] The sipe body 76 shown in FIG. 6 has a portion (hereinafter referred to as the upper straight portion 82) that extends straight in the depth direction from the groove opening 74M. The upper straight portion 82 is a portion of the sipe body 76 that has a uniform groove width WL1 in the depth direction. The sipe body 76 includes the upper straight portion 82 that has a uniform groove width WL1 in the depth direction. This upper straight portion 82 extends straight in the depth direction and length direction. The upper straight portion 82 is a two-dimensional sipe that spreads out like a flat plate. In FIG. 6, the position indicated by the symbol Y1 is the radially inner end of the upper straight portion 82. Although not shown, the upper straight portion 82 may be a three-dimensional sipe that extends in a zigzag pattern in the depth direction and length direction.

[0103] The tubular portion 78 is located radially inward of the sipe body 76. As described above, the tubular portion 78 includes the groove bottom 74T of the lateral sipe 74. In FIG. 6 , the position indicated by the symbol Y2 is the boundary between the tubular portion 78 and the second inflection portion 80. The length indicated by the double-headed arrow WL2 is the maximum width of the tubular portion 78. The position indicated by the symbol PY is the position where the tubular portion 78 exhibits the maximum width WL2 (hereinafter referred to as the maximum width position). The tubular portion 78 tapers outward from the portion exhibiting the maximum width WL2. The tubular portion 78 tapers inward from the portion exhibiting the maximum width WL2. In the outline of the tubular portion 78 shown in Figure 6, the portion indicating the maximum width WL2 is represented by a straight line, and the sipe body 76 side and the groove bottom 74T side of this straight line are represented by arcs. This tubular portion 78 has a track-like cross-sectional shape. The cross-sectional shape of this tubular portion 78 may be circular or elliptical.

[0104] The portion of the tubular portion 78 that is represented by a straight line is also referred to as a lower straight portion 84. In FIG. 6 , arrow Rs indicates the radius of the arc that represents the outline of the tubular portion 78 on the sipe body 76 side of the lower straight portion 84. The portion of the tubular portion 78 that is represented by the arc of radius Rs is also referred to as an upper arc portion 86. Arrow Ru indicates the radius of the arc that represents the outline of the tubular portion 78 on the groove bottom 74T side of the lower straight portion 84. The portion of the tubular portion 78 that is represented by the arc of radius Ru is also referred to as a lower arc portion 88. The center of the arc defining the outline of the upper arc portion 86 and the center of the arc defining the outline of the lower arc portion 88 are located on the centerline LY of the lateral sipe 74. Twice the radius Rs of the arc defining the outline of the upper arc portion 86 and twice the radius Ru of the arc defining the outline of the lower arc portion 88 are equal to the maximum width WL2 of the tubular portion 78.

[0105] The second inflection portion 80 connects the sipe main body 76 and the tubular portion 78. The groove width of the second inflection portion 80 gradually increases from the sipe main body 76 toward the tubular portion 78. The second inflection portion 80 curves so as to recess inward from its outer side. Specifically, in the cross section of the lateral sipe 74, the outline of the second inflection portion 80 is represented by a circular arc. In FIG. 6, arrow RL1 indicates the radius of the arc representing the outline of the second inflection portion 80. In the cross section of the lateral sipe 74 shown in FIG. 6 , the portion represented by the arc of radius RL1 is also referred to as the second boundary arc portion 90. The radially inner end Y1 of the upper straight portion 82 described above is also the radially outer end of the second boundary arc portion 90. Position Y1 is the boundary between the upper straight portion 82 and the second boundary arc portion 90. The arc representing the outline of the second boundary arc portion 90 is tangent to the straight line representing the outline of the upper straight portion 82 at boundary Y1. The boundary Y2 between the second inflection portion 80 and the tubular portion 78 described above is the radially inner end of the second boundary arc portion 90. The radially inner end Y2 is the boundary between the second boundary arc portion 90 and the tubular portion 78. The arc representing the outline of the second boundary arc portion 90 is tangent to the arc representing the outline of the upper arc portion 86 of the tubular portion 78 at boundary Y2.

[0106] 6, the length indicated by the double-headed arrow D5 is the groove depth of the lateral sipe 74. The length indicated by the double-headed arrow D6 is the groove depth of the sipe body 76 of the lateral sipe 74. The groove depth D6 of the sipe body 76 is expressed as the distance in the depth direction from the groove opening 74M of the lateral sipe 74 to the boundary LM between the sipe body 76 and the second inflection portion 80.

[0107] The lateral sipes 74 are shallower than the circumferential narrow grooves 18. Specifically, the ratio D5 / D1 of the groove depth D5 of the lateral sipes 74 to the groove depth D1 of the circumferential narrow grooves 18 is 0.50 or more and 1.00 or less.

[0108] The tread 4 of this tire 2 is formed with a plurality of circumferential grooves 10, a plurality of lateral grooves 32, and a plurality of lateral sipes 74. The tread 4 has a tread pattern including a plurality of circumferential grooves 10, a plurality of lateral grooves 32, and a plurality of lateral sipes 74. The tire 2 having such a tread pattern is manufactured as follows.

[0109] [Tire manufacturing method] In a tire manufacturing method according to one embodiment of the present invention, a green tire (a tire in an uncrosslinked state) is prepared by combining elements such as a tread and a sidewall that have been prepared as components. The green tire is placed in a tire mold, which will be described later, and the green tire is pressurized and heated in the mold. This crosslinks the uncrosslinked rubber composition contained in the green tire, and a tire that is a crosslinked product of the green tire is obtained. The method for manufacturing a tire includes the steps of providing a green tire and pressurizing and heating the green tire in a mold. In the present invention, pressurizing and heating a green tire in a mold is also called vulcanization molding, and the process of pressurizing and heating a green tire in a mold is also called a vulcanization process. In this production method, there are no particular limitations on production conditions such as vulcanization temperature and vulcanization time, and general tire production conditions are applied.

[0110] [Vulcanizer] In the vulcanization process, a vulcanizer 102 shown in Fig. 7 is used. An overview of the vulcanizer 102 will be described below, and for ease of explanation, the configuration of the vulcanizer 102 and the mold 104 set in this vulcanizer 102 will be expressed using the dimensions of the tire 2.

[0111] A mold 104 is incorporated into the vulcanizer 102. The vulcanizer 102 includes the mold 104 and a bladder 106. The configuration of the vulcanizer 102 other than the mold 104 is the same as that of a conventional vulcanizer. A detailed description of the components other than the mold 104 will be omitted.

[0112] As shown in Fig. 7, a green tire 2r for the tire 2 described above is placed in a cavity 108 formed between the mold 104 and the bladder 106. The green tire 2r is pressurized and heated in the cavity 108. This results in a tire 2 having the tread pattern shown in Fig. 1. This mold 104 is a mold for forming the tire 2, that is, a tire mold.

[0113] The mold 104 has an inner surface that is provided with a cavity surface 112. The cavity surface 112 abuts against the outer surface of the green tire 2r and shapes the outer surface of the tire 2 into the green tire 2r. The bladder 106 is located inside the mold 104. The bladder 106 is made of cross-linked rubber. A heating medium such as steam is filled inside the bladder 106, which causes the bladder 106 to expand. The bladder 106 shown in FIG. 7 is in an expanded state filled with the heating medium. The bladder 106 abuts against the inner surface of the green tire 2r, and shapes the inner surface of the tire 2 to the inner surface of the green tire 2r. The aforementioned cavity 108 is a space surrounded by the cavity surface 112 of the mold 104 and the bladder 106 . In this tire manufacturing method, a metal rigid core (not shown) may be used in place of the bladder 106. The rigid core has a toroidal outer surface that approximates the shape of the inner surface of the tire 2 when it is filled with air and its internal pressure is maintained at 5% of the normal internal pressure.

[0114] [Mold] The mold 104 shown in Figure 7 is a split mold type mold. The mold 104 includes, as its components, a tread ring 114, a pair of side plates 116, and a pair of bead rings 118. The aforementioned cavity surface 112 is formed by combining these components. The mold 104 in Figure 7 shows these components combined, in other words, in a closed state.

[0115] The tread ring 114 forms a tread portion T of the tire 2. Each side plate 116 forms a sidewall portion S of the tire 2. Each bead ring 118 forms a bead portion B of the tire 2. As previously mentioned, the tread portion T includes the tread 4. The tread ring 114 forms the tread 4.

[0116] 8 shows the tread ring 114. The position indicated by the symbol TRC in FIG. 8 is the center of the tread ring 114. The center TRC corresponds to the rotation axis of the tire 2.

[0117] The tread ring 114 has a plurality of segments 120. The plurality of segments 120 are arranged in the circumferential direction. The tread ring 114 is formed by combining a plurality of segments 120. Each segment 120 has a mating surface 122 that comes into close contact with an adjacent segment 120. In the tread ring 114, the portion where the segments 120 come into close contact with each other is the dividing surface 124. The dividing surface 124 is formed by the mating surfaces 122 of adjacent segments 120 coming into close contact with each other.

[0118] The tread ring 114 has a pattern forming portion 136 on its inner circumferential surface. The pattern forming portion 136 shapes the outer circumferential surface of the tread portion T, more specifically, the tread surface 6. This forms a tread pattern in the tread 4. The tread ring 114 has the pattern forming portion 136 that forms the tread pattern. As described above, the portions where the segments 120 are in close contact with each other are the dividing surfaces 124. The dividing surfaces 124 cross the pattern forming section 136. The tread ring 114 has a plurality of dividing surfaces 124. The plurality of dividing surfaces 124 divide the tread ring 114 into a plurality of segments 120. As a result, the pattern forming portion 136 is divided into a plurality of partial forming portions 138. Each of the plurality of segments 120 includes a partial forming portion 138 .

[0119] The vulcanizer 102 further includes an opening / closing frame 126 that opens and closes the mold 104 . The opening / closing frame 126 includes a plurality of sector shoes 128, an actuator 130, an upper holding plate 132, and a lower holding plate 134. Each of the multiple sector shoes 128 is located radially outside the corresponding segment 120. One segment 120 is fixed to one sector shoe 128. The number of sector shoes 128 is the same as the number of segments 120. The actuator 130 is ring-shaped. The actuator 130 is located radially outside the sector shoe 128. The sector shoe 128 is slidably connected to the actuator 130. Although not described in detail, the actuator 130 is movable up and down. The upper support plate 132 is disk-shaped. The upper side plate 116 and the bead ring 118 are fixed to this upper support plate 132. Although not described in detail, the upper support plate 132 is movable up and down. The lower support plate 134 is disk-shaped. The lower side plate 116 and the bead ring 118 are fixed to this lower support plate 134. Although not shown, the lower support plate 134 is fixed to the frame of the vulcanizer 102.

[0120] 7, when the vulcanization process is completed, the actuator 130 is raised, causing the sector shoes 128 to move radially outward. Because the segments 120 are fixed to the sector shoes 128, this causes the segments 120 to move radially outward as shown in FIG. 8. The multiple segments 120 that make up the tread ring 114 are movable radially. Then, the upper holding plate 132 is raised, causing the upper side plate 116 and the bead ring 118 to move upward. Then, the actuator 130 is further raised, causing the segments 120 to move upward together with the sector shoes 128. This opens the mold 104, and the tire 2 is removed.

[0121] In the vulcanization process, the green tire 2r is placed into the open mold 104. The green tire 2r is placed on the lower side plate 116 and the bead ring 118. The actuator 130 is lowered, and the segments 120 are moved downward together with the sector shoes 128. The upper holding plate 132 is then lowered, and the upper side plate 116 and the bead ring 118 are moved downward. The actuator 130 is then further lowered, and the segments 120 are moved radially inward together with the sector shoes 128. This closes the mold 104, and the green tire 2r is pressurized and heated.

[0122] In the vulcanization process, the green tire 2r is pressed against the pattern forming portion 136 of the tread ring 114. As a result, a tread pattern is formed in the tread 4 of the green tire 2r.

[0123] Figure 9 is a development view showing a part of the pattern forming portion 136. The tread pattern shown in Figure 1 is formed by this pattern forming portion 136. The pattern forming portion 136 has a concave-convex pattern corresponding to the tread pattern. In Figure 9, the dashed dotted line ELm corresponds to the equatorial plane EL of the tire 2. The dashed dotted line ELm is also called the corresponding equatorial plane. The position indicated by the symbol TEL is a position corresponding to the edge TE of the tread surface 6. The position TEL is also called the corresponding tread surface edge.

[0124] As described above, grooves 8 are formed in the tread 4 of the tire 2. The grooves 8 are formed by ridges 140. The pattern forming portion 136 of the tread ring 114 has ridges 140 that form the grooves 8. The tread pattern shown in FIG. 1 includes circumferential main grooves 16, circumferential narrow grooves 18, lateral grooves 32, and lateral sipes 74. The pattern forming portion 136 includes main groove ridges 142 that form the circumferential main grooves 16, narrow groove ridges 144 that form the circumferential narrow grooves 18, lateral groove ridges 146 that form the lateral grooves 32, and lateral blades 150 that form the lateral sipes 74.

[0125] Fig. 10 is a cross-sectional view taken along line XX in Fig. 9. Fig. 10 shows a cross section of the narrow groove ridge 144 taken along a plane perpendicular to the longitudinal direction of the narrow groove ridge 144. The cross-sectional shape of the narrow groove ridge 144 reflects the cross-sectional shape of the circumferential narrow groove 18 shown in Fig. 4.

[0126] The surface indicated by the symbol BL is a reference surface of the pattern forming portion 136. The reference surface BL is a surface corresponding to a virtual tread surface obtained assuming that the tread 4 does not have the grooves 8. The narrow groove ridge 144 protrudes from the reference plane BL. The tip PHT of the narrow groove ridge 144 corresponds to the groove bottom 18T of the circumferential narrow groove 18. The narrow groove ridge 144 has a base 152 and a bulge 154. The base 152 forms the body 54 of the circumferential narrow groove 18. The bulge 154 forms the first inflection portion 58 and the widened portion 56 of the circumferential narrow groove 18.

[0127] Figure 11 is a cross-sectional view taken along line XI-XI in Figure 9. Figure 11 shows a cross-section of the lateral blade 150 taken along a plane perpendicular to the longitudinal direction of the lateral blade 150. The cross-sectional shape of the lateral blade 150 reflects the cross-sectional shape of the lateral sipe 74 shown in Figure 6.

[0128] The lateral blade 150 protrudes from the reference plane BL of the pattern forming portion 136. A tip PBT of the lateral blade 150 corresponds to the groove bottom 74T of the lateral sipe 74. The lateral blade 150 includes a blade body 156 and a bar-shaped portion 158. The blade body 156 forms the sipe body 76 of the lateral sipe 74. The bar-shaped portion 158 forms the second inflection portion 80 and the tubular portion 78 of the lateral sipe 74.

[0129] When the green tire 2r is placed in the mold 104, the mold 104 is closed. At this time, the segments 120 move radially inward. As a result, the green tire 2r is pressed against the pattern forming portion 136 of the tread ring 114. The main groove ridges 142, narrow groove ridges 144, lateral groove ridges 146, and lateral blades 150 are inserted into the tread 4 of the green tire 2r. After the vulcanization process is completed, the mold 104 is opened to release the tire 2r from the mold 104. At this time, as shown in FIG. 8 , the segments 120 move radially outward. As a result, the narrow groove ridges 144 and lateral blades 150 are pulled out from the tread 4. The tire 2 is released from the mold 104.

[0130] In this tire 2, when the tread 4 comes into contact with the road surface and deforms, a pair of wall surfaces 18S of the circumferential narrow groove 18 come into contact with each other at the narrow groove portion 62. The two inner land portions 30 arranged on either side of the circumferential narrow groove 18 support each other, suppressing deformation of the inner land portions 30. This tire 2 can reduce rolling resistance. The sipe bodies 76 of the lateral sipes 74 can function as edge components. The tire 2 can maintain good wet performance even when the tread 4 is worn. The maximum width WC2 of the widened portions 56 of the circumferential narrow grooves 18 is wider than the minimum width WC1 of the narrow groove portions 62, and the maximum width WL2 of the tubular portions 78 of the lateral sipes 74 is wider than the minimum width WL1 of the sipe bodies 76. The widened portions 56 of the circumferential narrow grooves 18 and the tubular portions 78 of the lateral sipes 74 can contribute to ensuring groove volume. Even if the tread 4 wears and the sipe bodies 76 disappear, the exposed tubular portions 78 and widened portions 56 can contribute to maintaining wet performance. This tire 2 can maintain good wet performance from a new state until the tire 2 needs to be replaced. The tire 2 can suppress deterioration of wet performance due to wear and reduce rolling resistance.

[0131] As described above, the tread ring 114 of the mold 104 for this tire 2 includes the narrow groove ridges 144 that form the circumferential narrow grooves 18 and the lateral blades 150 that form the lateral sipes 74. After the vulcanization process is completed, the tire 2 is released from the mold 104. At this time, the narrow groove ridges 144 and the lateral blades 150 are pulled out from the tread 4. As described above, the lateral sipes 74 of this tire 2 are connected to the circumferential narrow grooves 18. This mold 104 has a connection portion between the narrow groove ridges 144 and the lateral blades 150, i.e., a ridge-blade connection portion. When the tire 2 is released from the mold 104, the rubber is likely to get caught at the ridge-blade connection portion. Stress is concentrated at the portion in contact with this connection portion, and depending on the extent of the stress, there is a concern that tread chipping may occur.

[0132] In this tire 2, the contour of the first inflection portion 58 of the circumferential narrow groove 18 and the contour of the second inflection portion 80 of the lateral sipe 74 are expressed by a single circular arc. The first inflection portion 58 and the second inflection portion 80 are configured with smooth shapes. Despite the fact that the circumferential narrow groove 18 has the widened portion 56 and the lateral sipe 74 has the tubular portion 78, the resistance force when the narrow groove ridge 144 and the lateral blade 150 are pulled out of the tread 4 is reduced. In particular, because the radius RC1 of the circular arc that expresses the contour of the first inflection portion 58 is larger than half the maximum width WC2 of the widened portion 56, the resistance force when the narrow groove ridge 144 is pulled out of the tread 4 is effectively reduced, and the rubber is prevented from getting caught in the ridge-blade connection portion. This tire 2 can suppress the occurrence of tread chipping when released from the mold 104. This tire 2 can suppress the occurrence of tread chipping when released from the mold 104 and the deterioration of wet performance due to wear, and can reduce rolling resistance.

[0133] From the viewpoint of effectively suppressing the occurrence of tread chipping, the ratio RC1 / WC2 of the radius RC1 of the arc representing the outline of the first inflection portion 58 to the maximum width WC2 of the widened portion 56 is preferably 1.5 or greater and 10.0 or less, and more preferably 2.5 or greater and 7.5 or less.

[0134] The radius RL1 of the arc defining the contour of the second inflection portion 80 of the lateral sipe 74 is preferably larger than half the maximum width WL2 of the tubular portion 78. This effectively reduces the resistance when the lateral blade 150 is pulled out of the tread 4, and prevents the rubber from getting caught at the ridge-blade connection portion. The tire 2 can prevent tread chipping when released from the mold 104. From this perspective, the ratio RL1 / WL2 of the radius RL1 of the arc defining the contour of the second inflection portion 80 to the maximum width WL2 of the tubular portion 78 is preferably 0.6 or greater and 5.0 or less, and more preferably 1.0 or greater and 4.0 or less.

[0135] From the viewpoint of effectively suppressing the occurrence of tread chipping when releasing the tire 2 from the mold 104, it is more preferable that the radius RC1 of the arc representing the outline of the first inflection portion 58 is greater than half the maximum width WC2 of the widened portion 56, and that the radius RL1 of the arc representing the outline of the second inflection portion 80 of the lateral sipe 74 is greater than half the maximum width WL2 of the tubular portion 78.

[0136] The ratio WC1 / WC2 of the minimum width WC1 of the narrow groove portion 62 to the maximum width WC2 of the widened portion 56 is preferably 0.10 or more and 0.35 or less. By setting the ratio WC1 / WC2 to 0.10 or greater, the resistance force when the narrow groove ridge 144 is pulled out of the tread 4 is reduced. The rubber is prevented from getting caught at the ridge blade connection portion. This tire 2 can reduce stress concentration that occurs near the connection portion. This tire 2 can prevent tread chipping when released from the mold 104. From this viewpoint, it is more preferable that the ratio WC1 / WC2 is 0.15 or greater. By setting the ratio WC1 / WC2 to 0.35 or less, the groove volume of the widened portion 56 is maintained appropriately. Even if the tread 4 wears and the lateral sipes 74 disappear, the exposed widened portion 56 can contribute to maintaining wet performance. This tire 2 can suppress deterioration of wet performance due to wear. From this viewpoint, it is more preferable that the ratio W1 / W2 is 0.30 or less.

[0137] The minimum width WC1 of the narrow groove portion 62 is preferably 2.5 mm or less. This allows the pair of wall surfaces 18S of the circumferential narrow groove 18 to come into effective contact at the narrow groove portion 62 when the tread 4 comes into contact with the road surface and deforms. Deformation of the inner land portion 30 is suppressed. The tire 2 can reduce rolling resistance. From this viewpoint, the minimum width WC1 is more preferably 2.0 mm or less. From the viewpoint of effectively draining water present between the tread 4 and a wet road surface through the circumferential narrow groove 18, the minimum width WC1 is preferably 1.0 mm or more.

[0138] The ratio D2 / D1 of the groove depth D2 of the body portion 54 to the groove depth D1 of the circumferential narrow groove 18 is preferably 0.25 or more and 0.70 or less. By setting the ratio D2 / D1 to 0.25 or greater, the groove depth D2 of the trunk portion 54 is maintained appropriately. When the tread 4 comes into contact with the road surface and deforms, the pair of wall surfaces 18S of the circumferential narrow groove 18 can come into sufficient contact at the narrow groove portion 62. 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 resistance force when the narrow groove ridge 144 is pulled out of the tread 4 is reduced. The rubber is prevented from getting caught at the ridge blade connection portion. The stress concentration occurring near the connection portion is reduced. The tire 2 can suppress the occurrence of tread chipping when released from the mold 104. From this viewpoint, it is more preferable that the ratio D2 / D1 is 0.65 or less.

[0139] The ratio DF / D1 of the groove depth D4 of the funnel portion 60 to the groove depth D1 of the circumferential narrow groove 18 is preferably 0.12 or more and 0.14 or less. By setting the ratio D4 / D1 to 0.12 or more, the funnel portion 60 can effectively suppress the concentration of strain at the groove mouths 18M of the circumferential narrow grooves 18. This effectively suppresses the occurrence of damage such as chipping at the edges of the inner land portion 30. This tire 2 has good durability. Setting the ratio D4 / D1 to 0.14 or less maintains an appropriate length of the narrow groove portion 62. When the tread 4 comes into contact with the road surface and deforms, the pair of wall surfaces 18S of the circumferential narrow groove 18 can come into sufficient contact at the narrow groove portion 62. This tire 2 can reduce rolling resistance. From the viewpoint of being able to stably manufacture a tire 2 having low rolling resistance and good durability while suppressing the occurrence of tread chipping, it is more preferable that the ratio D2 / D1 is 0.25 or more and 0.70 or less, and that the ratio D4 / D1 is 0.12 or more and 0.14 or less.

[0140] Fig. 12 shows a portion of a cross section taken along line XII-XII in Fig. 2. Fig. 12 shows a cross section of the equatorial plane of the tire 2. The length indicated by the double arrow D5 in Fig. 12 is the groove depth of the lateral sipe 74.

[0141] The groove depth D5 of the lateral sipes 74 is deeper than the groove depth D2 of the trunk portion 54. This allows the lateral sipes 74 to function as edge components from the early to mid-stages of wear. This tire 2 can maintain good wet performance. The groove depth D5 of the lateral sipes 74 is shallower than the maximum width groove depth D3 of the widened portion 56. This reduces the impact of the lateral sipes 74 on the rigidity of the tread 4. The trunk portion 54 of the circumferential narrow groove 18 (specifically, the narrow groove portion 62) can effectively contribute to suppressing deformation of the inner land portion 30. This tire 2 can reduce rolling resistance. Furthermore, the length of the ridge-blade connecting portion in the mold 104 is set to an appropriate length. When the narrow groove ridge 144 and the lateral blade 150 are pulled out of the tread 4, the rubber is prevented from getting caught at the ridge-blade connecting portion. Stress concentration occurring near the connecting portion is reduced. This tire 2 can suppress the occurrence of tread chipping when released from the mold 104. This mold 104 can suppress the occurrence of tread chipping when releasing a tire 2 having circumferential narrow grooves 18 and lateral sipes 62, which can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. From this perspective, it is preferable that the groove depth D2 of the body portion 54 of the circumferential narrow groove 18, the maximum width groove depth D3 of the widened portion 56, and the groove depth D5 of the lateral sipes 74 satisfy the following formula: Formula:D2 <D5<D3

[0142] When the groove depth D2 of the body portion 54, the maximum width groove depth D3 of the widened portion 56, and the groove depth D5 of the lateral sipes 74 satisfy the above formula, the occurrence of tread chipping when the tire 2 is released from the mold 104 is suppressed, and furthermore, from the viewpoint that the tire 2 can suppress deterioration of wet performance due to wear and reduce rolling resistance, it is more preferable that the ratio D2 / D5 of the groove depth D2 of the body portion 54 to the groove depth D5 of the lateral sipes 74 is 0.40 or more and 0.90 or less, and that the ratio D3 / D5 of the maximum groove depth D3 of the widened portion 56 to the groove depth D5 of the lateral sipes 74 is 1.05 or more and 2.00 or less.

[0143] The ratio (D6 / D5) of the groove depth D6 of the sipe body 76 of the lateral sipe 74 to the groove depth D5 of the lateral sipe 74 is preferably 0.55 or greater and 0.75 or less. By setting the ratio (D6 / D5) to 0.55 or greater, the effect of the tubular portion 78 on the rigidity of the inner block 34u is suppressed. Deformation of the inner block 34u is suppressed. The tire 2 can reduce rolling resistance. Because the tubular portion 78 can be exposed at an appropriate timing, the tire 2 can suppress deterioration of wet performance due to wear. From this viewpoint, it is more preferable that the ratio (D6 / D5) be 0.60 or greater. Setting the ratio (D6 / D5) to 0.75 or less appropriately maintains the groove volume of the tubular portion 78. This tire 2 can suppress deterioration of wet performance due to wear. From this viewpoint, the ratio (D6 / D5) is more preferably 0.70 or less.

[0144] The ratio WL2 / WL1 of the maximum width WL2 of the tubular portion 78 to the minimum width WL1 of the sipe body 76 is preferably 4 or greater, and more preferably 5 or greater. This allows the tubular portion 78 to contribute to maintaining wet performance. This ratio WL2 / WL1 is preferably 13 or less, and more preferably 12 or less. This allows the groove volume of the tubular portion 78 to be appropriately maintained. The effect of the tubular portion 78 on the rigidity of the inner block 34u is suppressed.

[0145] The maximum width WC2 of the widened portion 56 is preferably wider than the maximum width WL2 of the tubular portion 78. This ensures an appropriate groove volume in the middle stage of wear when the tubular portion 78 is exposed, and in the final stage of wear when the widened portion 56 is exposed, thereby enabling the tire 2 to effectively suppress deterioration of wet performance due to wear. From this viewpoint, the ratio WC2 / WL2 of the maximum width WC2 of the widened portion 56 to the maximum width WL2 of the tubular portion 78 is preferably equal to or greater than 1.2, and more preferably equal to or greater than 1.6. From the viewpoint of appropriately suppressing bulging of the widened portion 56 and suppressing the occurrence of tread chipping due to rubber getting caught at the ridge-blade connection portion when the narrow groove ridge 144 and the transverse blade 150 are pulled out of the tread 4, the ratio WC2 / WL2 is preferably equal to or less than 3.2, and more preferably equal to or less than 2.8.

[0146] 2, the angle β represents the angle formed by the longitudinal direction of the lateral sipes 74 with respect to the axial direction. In the present invention, this angle β is the inclination angle of the lateral sipes 74. In this tire 2, the inclination angle β of the lateral sipes 74 is preferably equal to or greater than −35 degrees and equal to or less than 35 degrees. In this case, stress concentration occurring near the connection portion of the ridge blade is suppressed when the narrow groove ridge 144 and the lateral blade 150 are pulled out of the tread 4. This tire 2 can suppress the occurrence of tread chipping when released from the mold 104. From this viewpoint, the inclination angle β is more preferably equal to or greater than −25 degrees and equal to or less than 25 degrees.

[0147] The narrow groove ridges 144 and the lateral blades 150 provided on each segment 120 constituting the tread ring 114 protrude inward. As described above, when the tire 2 is released from the mold 104, the segments 120 are moved radially outward. The narrow groove ridges 144 and the lateral blades 150 move together with the segments 120. The segments 120 have a predetermined length in the circumferential direction. A misalignment occurs between the protruding direction of the narrow groove ridges 144 and the lateral blades 150 and the direction of their movement.

[0148] Fig. 13 is a diagram illustrating the relationship between the protruding direction of the lateral blade 150 and the moving direction of the segment 120. Fig. 13 is a schematic diagram illustrating a cross section of the tread ring 114 along the corresponding equatorial plane ELm. 13, the orientation of the solid line LM corresponds to the movement direction of the segment 120. The orientation of the solid line LR represents the orientation of the lateral blade 150 provided on the segment 120, specifically, the orientation of the blade body 156. The solid line LRc represents the orientation of the lateral blade 150c located at the circumferential center of the segment 120. The solid line LRe represents the orientation of the lateral blade 150e located near the circumferential end of the segment 120, in other words, the dividing surface 124 of the tread ring 114.

[0149] 13, at the circumferential center of the segment 120, the orientation LRc of the lateral blade 150c coincides with the moving direction LM of the segment 120. The orientation of the lateral blade 150e closer to the dividing surface 124 does not coincide with the moving direction LM of the segment 120. The closer to the dividing surface 124, the more the orientation of the lateral blade 150 deviates from the moving direction LM of the segment 120. This deviation increases the resistance force when the narrow groove ridge 144 or the lateral blade 150 is pulled out of the tire 2. When the tire 2 is released from the mold 104, the stress acting on the land portion 20 is higher the closer it is to the parting surface 124. Near the parting surface 124, the stress acting on the land portion 20 is concentrated near the connection portion of the protruding blade, and depending on the degree of stress, there is a concern that tread chipping may occur.

[0150] In Figure 13, angle θ is the angle between solid lines LM and LR. In the present invention, this angle θ is the angle that the horizontal blade 150 forms with respect to the moving direction of the segment 120. The angle θ is 0 degrees at the circumferential center of the segment 120, but the angle θ increases as it approaches the dividing surface 124. In Figure 13, angle θx represents the angle that the horizontal blade 150 closest to the dividing surface 124 forms with respect to the moving direction of the segment 120, among all the horizontal blades 150 provided on each segment 120.

[0151] In this tire manufacturing method, in each segment, the angle θx that the lateral blade 150 closest to the dividing surface 124 makes with respect to the moving direction of the segment 120 is preferably 15 degrees or less.

[0152] In a conventional mold, the number of segments constituting a tread ring, i.e., the number of divisions of the tread ring, is set to 8 to 10. When the number of divisions of the tread ring 114 is set as in a conventional mold, the angle θx that the lateral blade 150 closest to the dividing surface 124 makes with respect to the moving direction of the segments 120 is 18.0 to 22.5 degrees. In contrast, in the mold 104 used in this manufacturing method, the angle θx that the lateral blade 150 closest to the dividing surface 124 makes with respect to the moving direction of the segments 120 is set to 15 degrees or less. The deviation between the orientation of the lateral blade 150 and the moving direction LM of the segments 120 is reduced. This manufacturing method reduces the resistance force when the narrow groove ridges 144 or the lateral blades 150 are pulled out of the tire 2. This manufacturing method can prevent rubber from getting caught at the ridge-blade connection portions. This manufacturing method can reduce stress concentration that occurs near the ridge-blade connection portions. This manufacturing method can prevent tread chipping when the tire 2 is released. From this viewpoint, in each segment 120 constituting the tread ring 114, the angle θx that the lateral blade 150 closest to the dividing surface 124 makes with respect to the moving direction of the segment 120 is preferably 15 degrees or less.

[0153] The number of segments 120 included in the tread ring 114 of this mold 104 is 17 or more. As a result, this manufacturing method allows the aforementioned angle θx to be set to 10.6 degrees or less. This manufacturing method allows the angle θx to be set even smaller, thereby further reducing the deviation between the orientation of the lateral blade 150 and the moving direction LM of the segments 120. This manufacturing method can reduce stress concentration that occurs near the connecting portion of the ridge blades due to the deviation between the protruding direction of the lateral blade 150 and the moving direction of the segments 120. This manufacturing method can suppress the occurrence of tread chipping when the tire 2 is released. From this perspective, the number of segments 120 included in the tread ring 114 is preferably 17 or more, and more preferably 19 or more. From the perspective of easy maintenance of the segments 120, the number of segments 120 is preferably 23 or less.

[0154] As shown in FIG. 7, the segment 120 constituting the tread ring 114 includes a main body 170 and a holder 172 that holds the main body 170. As described above, the tread ring 114 is formed by combining a plurality of segments 120. This forms a main body ring 174 made up of a plurality of main bodies 170 lined up in the circumferential direction, and a holder ring 176 made up of a plurality of holders 172 lined up in the circumferential direction. The main body ring 174 has the pattern forming portion 136 described above.

[0155] 9, the concave-convex pattern of the pattern forming portion 136 is divided into a plurality of pitch patterns 178 arranged in the circumferential direction. A solid line BP extending in the axial direction in FIG. 9 is a boundary between two adjacent pitch patterns 178. The concave-convex pattern of the pattern forming portion 136 that forms the tread pattern is formed by combining a plurality of pitch patterns 178. In the present invention, a pitch pattern means a unit pattern that is repeated in the circumferential direction.

[0156] As described above, the main body ring 174 has the pattern forming portion 136. The main body ring 174 has a plurality of pitch patterns 178 arranged in the circumferential direction. As shown in Fig. 14 , the plurality of pitch patterns 178 constituting the main body ring 174 include pitch patterns 178 where the dividing surfaces 124 of the tread ring 114 intersect (hereinafter referred to as boundary pitch patterns 178b) and pitch patterns 178 where the dividing surfaces 124 do not intersect (hereinafter referred to as normal pitch patterns 178n).

[0157] The dividing surface 124 crosses the boundary pitch pattern 178b that forms part of the pattern forming section 136. As shown in Fig. 9, the dividing surface 124 of this mold 104 is represented by a straight line extending in the axial direction.

[0158] When the lateral blade 150 intersects with the dividing plane 124, the lateral blade 150 is composed of two small blades. In this case, the rigidity of the entire lateral blade 150 decreases. A specific force tends to act on the lateral blade 150 located near the dividing surface 124, which may cause damage such as breakage or bending of the lateral blade 150 in addition to tread chipping. For this reason, the dividing surface 124 is positioned away from the lateral blade 150 so as not to intersect with the lateral blade 150.

[0159] 9, the length indicated by the double-headed arrow Lm is the shortest circumferential distance from the lateral blade 150 closest to the dividing surface 124 to the dividing surface 124. This shortest circumferential distance Lm is obtained by measuring the circumferential distance from the blade body 156 of the lateral blade 150 to the dividing surface 124.

[0160] The radius RC1 of the arc representing the contour of the first inflection portion 58 of the circumferential narrow groove 18 is larger than the shortest circumferential distance Lm. This reduces the resistance when the narrow groove ridge 144 is pulled out of the tread 4. It prevents the rubber from getting caught at the ridge-blade connection portion. It reduces stress concentration that occurs near the connection portion. This tire 2 can suppress the occurrence of tread chipping and blade damage when released from the mold 104. From this perspective, it is preferable that the radius RC1 of the arc representing the contour of the first inflection portion 58 is larger than the shortest circumferential distance Lm. Specifically, the ratio RC1 / Lm of the radius RC1 of the arc representing the contour of the first inflection portion 58 to the shortest circumferential distance Lm is preferably 1.1 or greater, and more preferably 1.5 or greater. From the viewpoint of properly maintaining the groove volume of the widened portion 56 and allowing the widened portion 56 to effectively contribute to maintaining wet performance, the ratio RC1 / Lm is preferably equal to or less than 8.0, and more preferably equal to or less than 7.0.

[0161] 15 is a development view showing a modified example (hereinafter, divided surface 124m) of the dividing surface 124. The concave-convex pattern of the pattern forming portion 136 shown in FIG.

[0162] The contour of the divided surface 124m shown in Fig. 15 includes three straight lines SL and two circular arcs AC. The three straight lines SL are aligned in the axial direction. The three straight lines SL are a first straight line SL1 including a first corresponding tread surface edge TEL1, a second straight line SL2 including a second corresponding tread surface edge TEL2, and a third straight line SL3 located between the first straight line SL1 and the second straight line SL2. The first straight line SL1 and the second straight line SL2 extend in the axial direction. The third straight line SL3 is inclined with respect to the axial direction. Two arcs AC each connect two adjacent straight lines SL. The two arcs AC are a first arc AC1 that connects the first straight line SL1 and the third straight line SL3, and a second arc AC2 that connects the second straight line SL2 and the third straight line SL3. An arrow Ra1 indicates the radius of the first arc AC1, and an arrow Ra2 indicates the radius of the second arc AC2.

[0163] As described above, the deviation between the protruding direction of the lateral blade 150 and the moving direction of the segment 120 is greatest at the circumferential end of the segment 120. Depending on the arrangement of the lateral blade 150, the parting surface 124 may be close to the lateral blade 150. In this case, when the tire 2 is released from the mold 104, stress is concentrated on the lateral blade 150 close to the parting surface 124, and depending on the degree of stress, tread chipping or blade damage may occur. However, if the contour of the dividing surface 124 includes at least one arc, the dividing surface 124 can be positioned away from the lateral blades 150, as in the dividing surface 124m shown in FIG. 14. This suppresses stress concentration on the lateral blades 150 close to the dividing surface 124. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this perspective, it is preferable that the contour of the dividing surface 124 includes at least one arc. In this case, it is more preferable that the radius of the arc is 5 mm or more.

[0164] As shown in Fig. 9, the horizontal blade 150 extends substantially in the axial direction. In Fig. 11, which shows a cross section of the horizontal blade 150, the direction indicated by the arrow WD1 is toward the dividing surface 124 and is called the circumferential end side of the segment 120. The direction indicated by the arrow WD2 is toward the circumferential center of the segment 120 and is called the circumferential center side of the segment 120. The lateral blade 150 has a first side surface 160 on the end side and a second side surface 162 on the center side. The tip PBT of the lateral blade 150 is the boundary between the first side surface 160 and the second side surface 162. The first side surface 160 and the second side surface 162 form the groove wall 74W of the lateral sipe 74.

[0165] As described above, a specific force tends to act on the rubber in contact with the lateral blade 150 located near the parting surface 124 (for example, the lateral blade designated by the symbol PL in FIG. 9 ) when it is pulled out of the tread 4. A force greater than that acting on the rubber in contact with the second side surface 162 on the center side acts on the rubber in contact with the first side surface 160 on the end side. There is a concern that the rubber in contact with the second side surface 162 on the center side is prone to chipping. The inventors have also considered the shape of the lateral blade 150 located near the parting surface 124 in order to suppress the occurrence of tread chipping when the tire 2 is released from the mold 104.

[0166] Figure 16 is a cross-sectional view taken along line XVI-XVI in Figure 9. Figure 16 shows a cross-section of the horizontal blade 150 provided in the segment 120, which is closest to the dividing surface 124. This horizontal blade 150 also includes a blade body 156 and a rod-shaped portion 158.

[0167] 16, the dashed dotted line LYm is the minimum width center line of the blade body 156. The minimum width center line LYm is represented by a line that passes through the center of the minimum width of the blade body 156 and extends in the direction in which the blade body 156 protrudes. The lateral blade 150 shown in Fig. 16 has a cross-sectional shape that is asymmetric with respect to the minimum width centerline LYm of the blade body 156. The lateral blade 150 having an asymmetric cross-sectional shape and closest to the dividing plane 124 is also referred to as a modified lateral blade 164 to distinguish it from the lateral blade 150 shown in Fig. 11. Unless otherwise specified, the components of the modified horizontal blade 164 that correspond to the components of the horizontal blade 150 in FIG. 11 are given the same reference numerals as the components of the horizontal blade 150, and the description thereof will be omitted.

[0168] Figure 17 is a cross-sectional view of the lateral sipe 74 (hereinafter, the modified lateral sipe 202) formed with the modified lateral blade 164 shown in Figure 16. Figure 17 shows a cross-section of the modified lateral sipe 202 along a plane perpendicular to the longitudinal direction of the modified lateral sipe 202. The modified lateral sipe 202 will be described below, but unless otherwise specified, the components of the modified lateral sipe 202 that correspond to the components of the lateral sipe 74 in Figure 6 will be given the same symbols as the symbols of the components of the lateral sipe 74, and their description will be omitted.

[0169] The modified lateral sipe 202 also has a pair of groove walls 202W connecting the groove mouth 202M and the groove bottom 202T. Of the pair of groove walls 202W of the modified lateral sipe 202 shown in FIG. 17 , the groove wall 202W located on the left side of the groove bottom 202T is formed by the first side surface 160 of the modified lateral blade 164. The groove wall 202W formed by the first side surface 160 is also referred to as the outer groove wall 202Ws. The groove wall 202W located on the right side of the groove bottom 202T is formed by the second side surface 162 of the modified lateral blade 164. The groove wall 202W formed by the second side surface 162 is also referred to as the inner groove wall 202Wu. The modified lateral sipe 202 has an outer groove wall 202Ws formed by a first side surface 160 of the modified lateral blade 164 on the dividing surface 124 side, and an inner groove wall 202Wu formed by a second side surface 162 located opposite the first side surface 160 of the modified lateral blade 164.

[0170] The modified lateral sipe 202 also includes a sipe body 76, a tubular portion 78, and a second inflection portion 80, similar to the lateral sipe 74 shown in FIG. The sipe body 76 of the modified lateral sipe 202 has an upper straight portion 82 that extends straight inward from the groove opening 202M. The sipe body 76 exhibits a minimum width WL1 at this upper straight portion 82. This upper straight portion 82 has a uniform groove width WL1 in its depth direction. 17, the position indicated by the symbol Y1s is the inner end of the upper straight portion 82 in the outer groove wall 202Ws, and the position indicated by the symbol Y1u is the inner end of the upper straight portion 82 in the inner groove wall 202Wu.

[0171] 17, the dashed dotted line LYc is the minimum width center line of the sipe body 76. The minimum width center line LYc passes through the center of the minimum width WL1 and extends in the depth direction of the deformed lateral sipe 202. The minimum width center line LYc passes through the groove bottom 202T of the deformed lateral sipe 202. The minimum width center line LYc corresponds to the center line LY of the lateral sipe 74 shown in FIG.

[0172] The tubular portion 78 of the modified lateral sipe 202 includes a groove bottom 202T. The tubular portion 78 is curved so as to bulge outward from the inside thereof. 17, the double-headed arrow WL2 represents the maximum width of the tubular portion 78. The maximum width WL2 is represented by the distance between the reference point PYs of the outer groove wall 202Ws and the reference point PYu of the inner groove wall 202Wu, measured, for example, along a line perpendicular to the minimum width center line LYc. The reference point PYs is the position where the distance from the minimum width center line LYc to the outer groove wall 202Ws is greatest in the tubular portion 78. In Figure 17, the distance from the minimum width center line LYc to the position PYs is represented by a double-headed arrow WL3. The reference point PYu is the position where the distance from the minimum width center line LYc to the inner groove wall 202Wu is greatest in the tubular portion 78. In Fig. 17, the distance from the minimum width center line LYc to the reference point PYu is represented by a double-headed arrow WL4. The maximum width WL2 of the tubular portion 78 of the modified lateral sipe 202 is expressed as the sum of the distance WL3 and the distance WL4.

[0173] The second inflection portion 80 connects the sipe main body 76 and the tubular portion 78. The portion of the modified lateral sipe 202 from the groove opening 202M to the boundary line LM is the sipe main body 76. 17, the position indicated by the symbol PMs is the intersection of the boundary line LM and the outer groove wall 202Ws. The position PMs is the boundary between the sipe main body 76 and the second inflection portion 80 in the outer groove wall 202Ws. The position indicated by the symbol PMu is the intersection of the boundary line LM and the inner groove wall 202Wu. The position PMu is the boundary between the sipe main body 76 and the second inflection portion 80 in the inner groove wall 202Wu.

[0174] The position indicated by the symbol Y2s is the boundary between the second inflection portion 80 on the outer groove wall 202Ws and the tubular portion 78. The position indicated by the symbol Y2u is the boundary between the second inflection portion 80 on the inner groove wall 202Wu and the tubular portion 78. The portion extending from the boundary Y2s to the boundary Y2u via the groove bottom 202T is the tubular portion 78. In this tire 2, the contour of the portion of the tubular portion 78 from the groove bottom 202T to the boundary Y2s is represented by an arc. Arrow Rus in FIG. 17 is the radius of this arc. The portion of the tubular portion 78 represented by the arc of radius Rus is also referred to as an outer lower arc portion 204. The contour of the portion of the tubular portion 78 from the groove bottom 202T to the boundary Y2u is also represented by an arc. Arrow Ruu in FIG. 17 is the radius of this arc. The portion of the tubular portion 78 represented by the arc of radius Ruu is also referred to as an inner lower arc portion 206. The center of the arc defining the contour of the outer lower circular arc portion 204 and the center of the arc of the inner lower circular arc portion 206 are located on the minimum width centerline LYc. The radius Rus of the arc defining the contour of the outer lower circular arc portion 204 is equal to the aforementioned distance WL3, and the radius Ruu of the arc defining the contour of the inner lower circular arc portion 206 is equal to the aforementioned distance WL4.

[0175] The portion of the outer groove wall 202Ws from the boundary PMs to the boundary Y2s is the portion of the outer groove wall 202Ws that corresponds to the second inflection portion 80 (hereinafter referred to as the outer second inflection portion corresponding portion 80s). The outer second inflection portion corresponding portion 80s curves so as to be recessed inward from the outside. Specifically, in the cross section of the deformed lateral sipe 202, the outline of the outer second inflection portion corresponding portion 80s is represented by a circular arc. In FIG. 17 , arrow RLs indicates the radius of the circular arc representing the outline of the outer second inflection portion corresponding portion 80s. In the tire 2, the portion represented by the arc of radius RLs is also referred to as an outer boundary arc portion 208. The arc representing the outline of the outer boundary arc portion 208 is tangent to a straight line representing the outline of the upper straight portion 82 in the outer groove wall 202Ws at position Y1s. Position Y1s is the boundary between the upper straight portion 82 and the outer boundary arc portion 208. This boundary Y1s is located radially outward of a boundary PMs between the sipe body 76 and the second inflection portion 80 in the outer groove wall 202Ws. This boundary Y1s and boundary PMs may coincide with each other. The arc representing the outline of the outer boundary arc portion 208 is tangent to the arc representing the outline of the outer lower arc portion 204 at position Y2s. Position Y2s is the boundary between the second inflection portion 80 and the tubular portion 78 in the outer groove wall 202Ws, and is also the boundary between the outer boundary arc portion 208 and the outer lower arc portion 204.

[0176] The portion of the inner groove wall 202Wu from the boundary PMu to the boundary Y2u is the portion of the inner groove wall 202Wu that corresponds to the second inflection portion 80 (hereinafter referred to as the inner second inflection portion corresponding portion 80s). The inner second inflection portion corresponding portion 80u curves so as to be recessed inward from its outer side. Specifically, the outline of the inner second inflection portion corresponding portion 80u is represented by a circular arc in the cross section of the deformed lateral sipe 74. In Figure 17, arrow R Lu indicates the radius of the circular arc representing the outline of the outer second inflection portion corresponding portion 80u. In the tire 2, the portion represented by the arc of radius RLu is also referred to as the inner boundary arc portion 210. The arc representing the outline of this inner boundary arc portion 210 is tangent to the straight line representing the outline of the upper straight portion 82 in the inner groove wall 202Wu at position Y1u. Position Y1u is the boundary between the upper straight portion 82 and the inner boundary arc portion 210. This boundary Y1u is located radially outward of the boundary PMu between the sipe main body 76 and the second inflection portion 80 in the outer groove wall 202Wu. This boundary Y1u and boundary PMu may coincide with each other. The arc representing the outline of the inner boundary arc portion 210 is tangent to the arc representing the outline of the inner lower arc portion 206 at position Y2u. Position Y2u is the boundary between the second inflection portion 80 and the tubular portion 78 in the inner groove wall 202Wu, and is also the boundary between the inner boundary arc portion 210 and the inner lower arc portion 206.

[0177] The modified lateral sipe 202 has a cross-sectional shape that is asymmetric with respect to the minimum width center line LYc of the sipe body 76. The maximum width center line LYe of the tubular portion 78 is located closer to the outer groove wall 202Ws than the minimum width center line LYc of the sipe body 76. In other words, the distance WL4 from the minimum width center line LYc to the position PYu at which the distance from the minimum width center line LYc to the inner groove wall 202Wu in the tubular portion 78 is greatest is shorter than the distance WL3 from the minimum width center line LYc to the position PYs at which the distance from the minimum width center line LYc to the outer groove wall 202Ws in the tubular portion 78 is greatest. This allows the tire 2 to reduce the amount of inward protrusion of the tubular portion 78, in other words, the amount of protrusion toward the center in the circumferential direction of the segment 120, while maintaining the maximum width WL2 of the tubular portion 78. By applying the modified lateral blade 164 that forms this modified lateral sipe 202 to the lateral blade 150 located near the dividing surface 124, the force acting on the rubber that contacts the center side of the segment 120, i.e., the second side surface 162 located opposite the dividing surface 124, is reduced when the tire 2 is released from the mold 104. This tire 2 can suppress the occurrence of tread chipping when released from the mold 104. Because the maximum width WL2 of the tubular portion 78 is maintained, the impact on wet performance caused by making the cross-sectional shape of the lateral sipe 74 asymmetrical is also suppressed. From this viewpoint, it is preferable that the lateral sipe 74 formed by the lateral blade 150 closest to the dividing surface 124 has a cross-sectional shape that is asymmetric with respect to the minimum width center line LYc of the sipe body 76, that this lateral sipe 74 has an outer groove wall 202Ws formed by the first side surface 160 on the dividing surface 124 side of the lateral blade 150, and an inner groove wall 202Wu formed by the second side surface 162 located opposite this first side surface 160, and that the maximum width center line LYe of the tubular portion 78 is located closer to the outer groove wall 202Ws than the minimum width center line LYc of the sipe body 76.

[0178] From the viewpoint of effectively suppressing the occurrence of tread chipping when releasing the tire 2 from the mold 104 while maintaining good wet performance, the ratio WL4 / WL3 of the distance WL4 from the minimum width center line LYc to the position PYu at which the distance from this minimum width center line LYc to the inner groove wall 202Wu in the tubular portion 78 is greatest to the distance WL3 from the minimum width center line LYc to the position PYs at which the distance from this minimum width center line LYc to the outer groove wall 202Ws in the tubular portion 78 is greatest is preferably 1.2 or greater and 3.3 or less, and more preferably 1.5 or greater and 3.0 or less.

[0179] The radius RLu of the arc representing the outline of the inner second inflection portion corresponding portion 80u is larger than the radius RLs of the arc representing the outline of the outer second inflection portion corresponding portion 80s. This reduces the force acting on the rubber that contacts the second side surface 162 located opposite the dividing surface 124 when the tire 2 is released from the mold 104. The tire 2 can suppress the occurrence of tread chipping when released from the mold 104. From this viewpoint, the ratio RLu / RLs of the radius RLu of the arc representing the outline of the inner second inflection portion corresponding portion 80u to the radius RLs of the arc representing the outline of the outer second inflection portion corresponding portion 80s is preferably 2.0 or greater and 17.0 or less, and more preferably 4.0 or greater and 14.0 or less.

[0180] 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 104 and the deterioration of wet performance due to wear, and can reduce rolling resistance. [Industrial Applicability]

[0181] 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 reduce rolling resistance, can be applied to various types of tires.

[0182] [Note] The present invention includes the following aspects.

[0183] [1] A tire has a tread that contacts a road surface at a tread surface, the tread having a tread pattern including a plurality of circumferential grooves and a plurality of lateral sipes, the plurality of circumferential grooves constituting a plurality of land portions in the tread, the plurality of land portions including a pair of outer land portions located axially outermost and including an edge of the tread surface, and a plurality of inner land portions located between the pair of outer land portions and aligned in the axial direction, the plurality of circumferential grooves including a circumferential main groove located between each of the outer land portions and the inner land portion located axially inside the outer land portion, and a circumferential narrow groove located between two adjacent inner land portions, the circumferential narrow groove having a body portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and a first inflection portion connecting the body portion and the widened portion, the body portion having a narrow groove portion, and a maximum width WC2 of the widened portion being equal to or smaller than the minimum width WC3 of the narrow groove portion. a tubular portion including a groove bottom of the lateral sipe; and a second inflection portion connecting the sipe body and the tubular portion, wherein the maximum width WL2 of the tubular portion is greater than the minimum width WL1 of the sipe body. A heavy-duty tire having a tire width of 100 mm or more and a width of 100 mm or more, the width of the tubular portion being 100 mm or more and a width of 100 mm or more. [2] The heavy-duty tire according to the above-mentioned [1], wherein a radius RL1 of the arc that defines the contour of the second inflection portion is greater than half the maximum width WL2 of the tubular portion. [3] The heavy-duty tire according to the above [1] or [2], wherein the ratio WC1 / WC2 of the minimum width WC1 of the narrow groove portion to the maximum width WC2 of the widened portion is 0.10 or more and 0.35 or less. [4] The heavy-duty tire according to any one of [1] to [3] above, wherein the narrow groove portion has a minimum width WC1 of 2.5 mm or less. [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 body portion of the circumferential narrow groove 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 D2 of the body portion of the circumferential narrow groove, a groove depth D3 from the groove mouth of the circumferential narrow groove to a position where the widened portion has a maximum width WC2, and a groove depth D5 of the lateral sipe satisfy the following formula: Formula:D2 <D5<D3 [7] a tread ring that forms the tread; a pattern forming portion that forms the tread pattern; the pattern forming portion including main groove ridges that form the circumferential main grooves, narrow groove ridges that form the circumferential narrow grooves, and lateral blades that form the lateral sipes; the tread ring that has a plurality of dividing surfaces that cross the pattern forming portion; the plurality of dividing surfaces that divide the tread ring into a plurality of segments that are aligned in the circumferential direction; the plurality of segments that are movable in the radial direction of the tire; and in each of the segments, an angle that the lateral blade closest to the dividing surface forms with respect to the moving direction of the segment is 15 degrees or less. [8] The method for manufacturing a heavy-duty tire according to the above-mentioned [7], wherein the number of the segments included in the tread ring is 17 or more. [9] The method for manufacturing a heavy-duty tire according to the above-mentioned [7] or [8], wherein the radius RC1 of the arc representing the outline of the first inflection portion is greater than the shortest distance from the lateral blade closest to the dividing surface to the dividing surface.

[10] The method for manufacturing a heavy-duty tire according to any one of [7] to [9] above, wherein, in a development view of the pattern forming portion, the outline of the dividing surface includes at least one arc.

[11] A method for manufacturing a heavy-duty tire as described in any of [7] to

[10] above, wherein the lateral sipe formed by the lateral blade closest to the dividing surface has a cross-sectional shape asymmetric with respect to the minimum width center line of the sipe body, the lateral sipe has an outer groove wall formed by a first side surface of the lateral blade on the dividing surface side, and an inner groove wall formed by a second side surface of the lateral blade located opposite to the first side surface, and the maximum width center line of the tubular portion is located closer to the outer groove wall than the minimum width center line of the sipe body. [Explanation of symbols]

[0184] 2. Tires 2r raw tires 4. Tread 6. Tread surface 10...Circumferential groove 18... Circumferential narrow groove 20... Rikubu 28...outer land area 30...inner land area 54 Torso 56 Widened section 58 First inflection 62...Narrow groove part 74 Lateral sipes 76···Sipe body 78...Tubular part 80...Second inflection part 104···Mold 114 Tread ring 116 Side Plate 120 segments 124...Divided plane 150, 150c, 150e... Horizontal blade 160...first side 162...Second side 202 Deformed lateral sipes

Claims

1. The tread surface is in contact with the road surface, the tread has a tread pattern including a plurality of circumferential grooves and a plurality of lateral sipes; a plurality of the circumferential grooves defining a plurality of land portions in the tread; the plurality of land portions include a pair of outer land portions located axially outermost and including edges of the tread surface, and a plurality of inner land portions located between the pair of outer land portions and aligned in the axial direction, the plurality of circumferential grooves include a circumferential main groove located between each of the outer land portions and an inner land portion located axially inside the outer land portion, and a circumferential narrow groove located between two adjacent inner land portions, the circumferential narrow groove includes a body portion including a groove mouth of the circumferential narrow groove, a widened portion including a groove bottom of the circumferential narrow groove, and a first inflection portion connecting the body portion and the widened portion, The body portion has a narrow groove portion, and a maximum width WC2 of the widened portion is wider than a minimum width WC1 of the narrow groove portion, When the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow groove come into contact with each other at the narrow groove portion, In a cross section of the circumferential narrow groove, a contour of the first inflection portion is represented by an arc having a radius RC1, At least one of the inner land portions has the lateral sipe, and the lateral sipe is connected to the circumferential narrow groove, The lateral sipe comprises a sipe body including a groove mouth of the lateral sipe, a tubular portion including a groove bottom of the lateral sipe, and a second inflection portion connecting the sipe body and the tubular portion, The maximum width WL2 of the tubular portion is wider than the minimum width WL1 of the sipe body, In the cross section of the lateral sipe, the outline of the second inflection portion is represented by an arc having a radius RL1, The radius RC1 of the arc representing the contour of the first inflection portion is greater than half the maximum width WC2 of the widened portion. Heavy duty tires.

2. a radius RL1 of the arc representing the contour of the second inflection portion is greater than half the maximum width WL2 of the tubular portion; 2. The heavy duty tire according to claim 1.

3. a ratio WC1 / WC2 of a minimum width WC1 of the narrow groove portion to a maximum width WC2 of the widened portion is 0.10 or more and 0.35 or less; 2. The heavy duty tire according to claim 1.

4. The minimum width WC1 of the narrow groove portion is 2.5 mm or less.

2. The heavy duty tire according to claim 1.

5. a ratio D2 / D1 of a groove depth D2 of the trunk portion of the circumferential narrow groove 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. The groove depth D2 of the body portion of the circumferential narrow groove, the groove depth D3 from the groove mouth of the circumferential narrow groove to the position where the widened portion shows the maximum width WC2, and the groove depth D5 of the lateral sipe satisfy the following formula:

2. The heavy duty tire according to claim 1. Formula: D2<D5<D3

7. A method for manufacturing a heavy duty tire according to any one of claims 1 to 6, pressurizing and heating a green tire for said tire in a mold; the mold includes a tread ring that forms the tread; The tread ring has a pattern forming portion that forms the tread pattern, The pattern forming portion includes a main groove ridge that forms the circumferential main groove, a narrow groove ridge that forms the circumferential narrow groove, and a lateral blade that forms the lateral sipe, The tread ring has a plurality of dividing surfaces that cross the pattern forming portion, The plurality of dividing surfaces divide the tread ring into a plurality of segments arranged in a circumferential direction, A plurality of the segments are movable in the radial direction of the tire, In each of the segments, the angle of the horizontal blade closest to the dividing surface with respect to the moving direction of the segment is 15 degrees or less. A method for manufacturing heavy-duty tires.

8. The number of the segments included in the tread ring is 17 or more. A method for manufacturing a heavy duty tire according to claim 7.

9. a radius RC1 of the arc representing the contour of the first inflection portion is greater than the shortest distance from the horizontal blade closest to the dividing surface to the dividing surface; A method for manufacturing a heavy duty tire according to claim 7.

10. In a development view of the pattern forming portion, the outline of the dividing surface includes at least one arc. A method for manufacturing a heavy duty tire according to claim 7.

11. The lateral sipe formed by the lateral blade closest to the parting surface has a cross-sectional shape that is asymmetric with respect to the minimum width centerline of the sipe body, The lateral sipe has an outer groove wall formed by a first side surface of the lateral blade on the dividing surface side, and an inner groove wall formed by a second side surface of the lateral blade located opposite to the first side surface, a maximum width center line of the tubular portion is located closer to the outer groove wall than a minimum width center line of the sipe body; A method for manufacturing a heavy duty tire according to claim 7.

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