Tire for heavy load

Abstract

To provide a tire 2 for heavy load that can suppress occurrence of tread separation when releasing from a mold, degradation of wet performance due to wear, and can achieve reduction of rolling resistance.SOLUTION: A tire 2 comprises a tread 4. The tread 4 has a circumferential direction main groove 14 and a circumferential direction narrow groove 20. A plurality of land parts 12 configured on the tread 4 includes a center land part 123. The center land part 123 has a traverse sipe 22. The circumferential direction narrow groove 20 is deeper than the traverse sipe 22. The circumferential direction narrow groove 20 includes a narrow groove part 16 and a widening part 18. The tread 4 deforms, whereby the inner groove wall 102Wu and the outer groove wall 102Ws of the circumferential direction narrow groove 20 contact at the narrow groove part 16. The maximum width of the widening part 18 is wider than the minimum width W1 of the narrow groove part 16. The widening part 18 has a shape asymmetric with respect to the minimum width center line NL of the narrow groove part 16. The maximum width center line WL of the widening part 18 is positioned on the axial direction outer side of the minimum width center line NL of the narrow groove part 16.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] The tread of a tire has a plurality of circumferential grooves arranged in parallel in the axial direction. The plurality of circumferential grooves constitute a plurality of land portions on the tread. When the land portion comes into contact with the road surface, it deforms. The deformation of the land portion affects the rolling resistance of the tire. Considering the impact on the environment, reducing the rolling resistance is strongly required for tires. By providing narrow-grooved portions with narrow groove widths in the circumferential grooves, the land portions can support each other when the tread contacts the road surface. Thereby, the deformation of the land portion is suppressed. In order to reduce the rolling resistance of the tire, the adoption of circumferential grooves having narrow-grooved portions, that is, circumferential narrow grooves, has been considered (for example, Patent Document 1 below).

[0003] A tire is obtained by vulcanizing a green tire in a mold. The tread ring of the mold shapes the outer surface of the tread. When engraving circumferential narrow grooves on the tread, the tread ring is provided with ridges reflecting the shape of the circumferential narrow grooves. The ridges protrude radially inward.

[0004] When the mold is a split mold, the tread ring is composed of a plurality of segments arranged in the circumferential direction. When the vulcanization process is completed, the tire is released from the mold. At this time, each segment is moved radially outward. Thereby, the ridges are pulled out from the tread.

[0005] Circumferential narrow grooves also affect, for example, the running performance on a wet road surface (hereinafter also referred to as wet performance). Improvements to circumferential narrow grooves are being made while considering the impact on various performances.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2017-094891 Summary of the Invention Problems 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 releasing from a mold and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance. Means for Solving the Problems

[0008] The heavy-duty tire according to the present invention includes a tread. The tread includes a tread surface that contacts the road surface. The tread includes a plurality of circumferential grooves that extend continuously in the circumferential direction. Thereby, a plurality of land portions arranged in the axial direction are formed. The plurality of circumferential grooves include a pair of circumferential main grooves and a pair of circumferential fine grooves located between the pair of circumferential main grooves. The plurality of land portions include a center land portion located between the pair of circumferential fine grooves, a pair of middle land portions located between the circumferential fine groove and the circumferential main groove located outside the axial direction of the circumferential fine groove, and a pair of shoulder land portions located outside the axial direction of the circumferential main groove. The center land portion has a transverse sipe that connects between the pair of circumferential fine grooves. Each of the pair of circumferential fine grooves is deeper than the transverse sipe. The circumferential fine groove includes a fine groove portion and a widened portion located radially inside the fine groove portion. When the tread contacts the road surface and deforms, the opposing inner groove wall and outer groove wall of the circumferential fine groove contact in the fine groove portion. The maximum width W of the widened portion is wider than the minimum width W1 of the fine groove portion. The widened portion has an asymmetrical shape with respect to the minimum width center line of the fine groove portion. The maximum width center line of the widened portion is located outside the axial direction of the minimum width center line of the fine groove portion. Effects of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

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

[0012] The tire of the present invention is assembled to a rim. The inside of the tire is filled with air and the internal pressure of the tire is adjusted. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire assembled to this rim.

[0013] In the present invention, a state where the tire is assembled to a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to this tire is called a standard state.

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

[0015] The regular rim means the rim defined 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 regular rims.

[0016] The regular internal pressure means the internal pressure defined in the standard on which the tire is based. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0017] The regular load means the load defined in the standard on which the tire is based. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0018] In the present invention, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of sidewall portions.

[0019] [Findings underlying the present invention] As described above, by providing circumferential narrow grooves in the tread, deformation of the land portion is suppressed when the tread contacts the road surface. By making a part of the circumferential grooves provided in the tread into circumferential narrow grooves, the tire can reduce rolling resistance. Circumferential narrow grooves are inferior in drainage performance compared to circumferential main grooves. When a part of the circumferential grooves provided in the tread is made into circumferential narrow grooves, there is a concern that the wet performance may deteriorate due to wear of the tread. Sipes (hereinafter referred to as transverse sipes) that cross the land portion can function as edge components. By providing transverse sipes in the land portion, the tire can suppress a decrease in wet performance. If a widened portion having a groove width wider than the groove width of the narrow groove portion is provided on the groove bottom side of the circumferential narrow groove, the widened portion can contribute to securing the groove volume. By exposing the widened portion, the tire can suppress a decrease in wet performance.

[0020] As a result of intensive studies on a tread pattern including circumferential narrow grooves and transverse sipes, the present inventors have found that by providing a transverse sipe so as to bridge between two circumferential narrow grooves and arranging the circumferential narrow grooves so that the widened portion is exposed when the transverse sipe disappears, the tire can reduce rolling resistance while suppressing a decrease in wet performance due to wear.

[0021] As described above, when circumferential narrow grooves are engraved in the tread, the tread ring of the mold is provided with ridges reflecting the shape of the circumferential narrow grooves. When a widened portion is provided in the circumferential narrow groove, the shape of the widened portion is reflected in the tip portion of the ridge. When the vulcanization process is completed and the tire is released from the mold, the tip portion passes through a narrow groove portion having a groove width narrower than that of the widened portion. The extraction of the ridge is accompanied by deformation of the land portion.

[0022] A blade is used to cut the sipe into the tread. In order to provide a transverse sipe so as to bridge between two circumferential grooves, the blade is disposed so as to bridge between two ridges. In a mold in which the blade is disposed in this way, when the ridge and the blade are pulled out from the tread, a part of the land portion tends to be caught at the connection portion between the ridge and the blade. The closer to the circumferential end of the segment, the more obliquely the ridge is pulled out with respect to its protruding direction. The strain generated in the land portion is large near the connection portion.

[0023] As described above, when the widened portion is provided in the circumferential groove, the shape of the widened portion is reflected in the tip portion of the ridge. The distance between the two ridges is narrow at the tip portion of the ridge. Therefore, while the two ridges press the land portion from both sides at their tip portions, the ridge is pulled out from the tread. If the pressing force by the ridge is strong, high stress is generated in the land portion formed between the two ridges. Depending on the degree of stress generated in the land portion, there is a concern that a chip may occur in the land portion.

[0024] Therefore, the present inventor has earnestly studied the shape of the circumferential groove in order to obtain a tire that can suppress the occurrence of tread chipping and the deterioration of wet performance due to wear when releasing from the mold, and can achieve a reduction in rolling resistance, and has completed the present invention described below.

[0025] [Outline of Embodiment of the Present Invention] The present invention relates to a tire having a tread, the tread having a tread surface that contacts the road surface, the tread having a plurality of circumferential grooves extending continuously in the circumferential direction, thereby forming a plurality of land portions arranged in the axial direction, the plurality of circumferential grooves including a pair of circumferential main grooves and a pair of circumferential fine grooves located between the pair of circumferential main grooves, the plurality of land portions including a center land portion located between the pair of circumferential fine grooves, a pair of middle land portions located between the circumferential fine grooves and the circumferential main grooves located outside the circumferential fine grooves in the axial direction, and a pair of shoulder land portions located outside the circumferential main grooves in the axial direction, the center land portion having a transverse sip that connects between the pair of circumferential fine grooves, the pair of circumferential fine grooves being deeper than the transverse sip respectively, the circumferential fine grooves including a fine groove portion and a widened portion located radially inside the fine groove portion, when the tread contacts the road surface and deforms, the opposing inner groove wall and outer groove wall of the circumferential fine groove contact in the fine groove portion, the maximum width W of the widened portion is wider than the minimum width W1 of the fine groove portion, the widened portion has an asymmetric shape with respect to the minimum width center line of the fine groove portion, and the maximum width center line of the widened portion is located outside the minimum width center line of the fine groove portion in the axial direction, which is a heavy-duty tire.

[0026] The heavy-duty tire of the present invention can suppress the occurrence of tread chipping when released from the mold and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance. Although the mechanism by which such an effect is achieved has not been clarified, it is speculated as follows.

[0027] When the tread contacts the road surface and deforms, the opposing inner groove wall and outer groove wall of the circumferential fine groove contact in the fine groove portion. The two land portions located on both sides of the circumferential fine groove support each other, and the deformation of the land portion is suppressed. This tire can reduce rolling resistance. The transverse sip functions as an edge component. This tire can maintain good wet performance even when the tread wears. The widened portion provided on the groove bottom side of the circumferential fine groove can contribute to ensuring the groove volume. Even when the tread wears and the transverse sip disappears, the exposed widened portion can contribute to maintaining wet performance. This tire can maintain good wet performance from the new state until the tire needs to be replaced. This tire can suppress the decrease in wet performance due to wear and achieve a reduction in rolling resistance.

[0028] The mold for this tire includes ridges that form circumferential grooves and blades that form transverse sipes, and the tip portions of the ridges form the widened portions of the circumferential grooves. When the vulcanization process is completed, the tire is released from the mold. At this time, the ridges and blades are pulled out from the tread.

[0029] In this tire, the widened portion of the circumferential groove has an asymmetric shape with respect to the center line of the minimum width of the groove portion, and the center line of the maximum width of the widened portion is located axially outside the center line of the minimum width of the groove portion. Thereby, the tire can reduce the amount of protrusion of the widened portion inward in the axial direction while maintaining the maximum width of the widened portion. When the ridges and blades are pulled out from the tread, the force with which the tip portions of the two ridges press against the center land portion is reduced. This tire can suppress the occurrence of tread chipping when releasing the tire from the mold. This tire can suppress the occurrence of tread chipping when releasing the tire from the mold and the decrease in wet performance due to wear, and can achieve a reduction in rolling resistance.

[0030] From the viewpoint of reducing rolling resistance, preferably, the minimum width W1 of the groove portion is 2.5 mm or less.

[0031] From the viewpoints of suppressing tread chipping and maintaining wet performance, preferably, the axial distance W2 from the outer groove wall at the minimum width position of the groove portion to the axially outer end of the widened portion is longer than the minimum width W1 of the groove portion, and the axial distance W2 is longer than the axial distance W3 from the inner groove wall at the minimum width position of the groove portion to the axially inner end of the widened portion.

[0032] From the viewpoint of suppressing tread chunking, preferably, the circumferential fine groove has a bent portion between the fine groove portion and the widened portion, and the contour of the portion of the inner groove wall corresponding to the bent portion and the contour of the portion of the outer groove wall corresponding to the bent portion are represented by a single arc.

[0033] From the viewpoints of suppressing tread chunking and maintaining wet performance, preferably, the radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion is larger than the radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion.

[0034] From the viewpoint of suppressing tread chunking, preferably, the angle formed by the transverse sipes with respect to the axial direction is -35 degrees or more and 35 degrees or less.

[0035] From the viewpoint of suppressing tread chunking, preferably, the ratio L2 / L1 of the width L2 of the center land portion to the width L1 of the middle land portion is 0.5 or more and 2.0 or less.

[0036] From the viewpoints of suppressing tread chunking and maintaining wet performance, preferably, the ratio W2 / W3 of the axial distance W2 from the outer groove wall to the axial outer end of the widened portion at the minimum width position of the fine groove portion to the axial distance W3 from the inner groove wall to the axial inner end of the widened portion at the minimum width position of the fine groove portion is 1.5 or more and 4.0 or less.

[0037] From the viewpoints of suppressing tread chunking and maintaining wet performance, preferably, the radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion is 2.0 mm or more, and the ratio R2 / R1 of the radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion to the radius R1 is 2.0 or more.

[0038] From the viewpoint of suppressing tread chunking, preferably, the virtual straight line parallel to the minimum width center line and including the inner groove wall at the minimum width position of the fine groove portion includes the axial inner end of the widened portion.

[0039] From the viewpoint of maintaining wet performance, preferably, the ratio W2 / W1 of the axial distance W2 from the outer groove wall at the minimum width position of the narrow groove portion to the axial outer end of the widened portion to the minimum width W1 of the narrow groove portion is 2.0 or more.

[0040] From the viewpoints of suppressing tread chipping, maintaining wet performance, and reducing rolling resistance, preferably, in the radial direction, the groove bottom of the transverse sipes is located between the boundary between the narrow groove portion and the bent portion on the inner groove wall and the axial inner end of the widened portion located radially inward of the boundary.

[0041] [Details of Embodiments of the Present Invention] FIG. 1 is a plan view showing a part of a tread 4 of a tire 2 according to an embodiment of the present invention. This tire 2 is mounted on a vehicle such as a truck or a bus. This tire 2 is a heavy-duty tire. In FIG. 1, the direction indicated by the double-headed arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis (not shown) of the tire 2. The direction indicated by the double-headed 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. The one-dot chain line EL extending in the circumferential direction in FIG. 1 represents the equatorial plane of the tire 2. In FIG. 1, the side indicated by the arrow AD1 is the first axial direction side of the tire 2, and the side indicated by the arrow AD2 is the second axial direction side of the tire 2. The side facing the equatorial plane in the axial direction is the axial inner side, and the side facing the end of the tread surface described later is the axial outer side. In FIG. 1, the side indicated by the arrow CD1 is the first circumferential direction side of the tire 2, and the side indicated by the arrow CD2 is the second circumferential direction side of the tire 2.

[0042] FIG. 1 shows a tread pattern formed on the tread 4. The tread pattern of the present invention will be described using this tread pattern as an example. In the present invention, the internal structure of the tire 2 is not particularly limited. Although not described in detail, this tire 2 has a general internal structure as an internal structure of a heavy-duty tire. The tread pattern in FIG. 1 is that of a new tire 2, i.e., the tread pattern of an unworn tread 4.

[0043] The tread 4 is located on the radially outer side of the tire 2 and extends in the circumferential direction. The outer peripheral surface of the tread 4 is the tread surface 6. The tire 2 contacts the road surface at the tread surface 6. The tread 4 has a tread surface 6 that contacts the road surface. The tread 4 is made of cross-linked rubber. Although not described in detail, the portion of the tread 4 including the tread surface 6 is composed of cross-linked rubber considering wear resistance and grip performance. The other portions are composed of cross-linked rubber with low heat generation. Grooves 8 are engraved in the tread 4. Thereby, the tread pattern is formed.

[0044] The intersection of the tread surface 6 and the equatorial plane is the equator Eq. When a groove 8 is located on the equatorial plane, the equator Eq is specified based on a virtual tread surface obtained by assuming that there is no groove 8 on the equatorial plane. The equator Eq is the radially outer end of the tire 2.

[0045] The solid line indicated by the symbol TE is the end of the tread surface 6. In the present invention, when the end TE of the tread surface 6 is indistinguishable in appearance, a normal load is applied to the tire in a normal state, the camber angle is set to 0°, and the position on the outer surface of the tire corresponding to the axially outer end of the contact surface obtained by bringing the tire into contact with a plane is the end of the tread surface.

[0046] In the tread surface 6 shown in FIG. 1, the end TE of the tread surface 6 located on the first axial direction AD1 side is the first end TE1. The end TE located on the second axial direction AD2 side is the second end TE2. The length indicated by the double arrow TW is the width of the tread surface 6. The width TW of the tread surface 6 is the axial distance from the first end TE1 to the second end TE2 of the tread surface 6. The width TW of the tread surface 6 is represented by the length measured along the tread surface 6.

[0047] Figure 2 is a cross-sectional view taken along line II-II of Figure 1. Figure 2 shows the cross-section of groove 8, specifically, the shoulder circumferential groove described later. Based on Figure 2, the main configuration of groove 8 will be described. In Figure 2, the direction indicated by the double arrow RD is the radial direction of tire 2. The side indicated by arrow RD1 is the outer side in the radial direction of tire 2, and the side indicated by arrow RD2 is the inner side in the radial direction of tire 2. In the present invention, the cross-section of groove 8 is represented by a cross-section along a plane perpendicular to the length direction of groove 8.

[0048] Groove 8 has a pair of groove walls 8W including groove opening 8M and a bottom surface 8B including groove bottom 8T. The groove width of groove 8 is represented by the distance between a first groove wall 8W and a second groove wall 8W, which are a pair of groove walls 8W, that is, the distance between the groove walls. In Figure 2, the length indicated by the double arrow WG is the groove width of groove 8 at groove opening 8M. Groove width WG is represented by the shortest distance between a pair of edges 8E that form groove opening 8M. When the portion of groove opening 8M of groove 8 is processed in a tapered manner, the groove width of groove 8 at groove opening 8M is represented based on a virtual edge obtained assuming it is not processed in a tapered manner. The length indicated by the double arrow DG is the groove depth of groove 8. The groove depth DG of groove 8 is represented by the shortest distance from the line segment connecting the left and right edges 8E to groove bottom 8T of groove 8. The position, groove width WG, and groove depth DG of groove 8 are appropriately determined according to the specifications of tire 2.

[0049] Groove bottom 8T is the deepest position in the cross-section of groove 8. Along the normal line of the line segment connecting the left and right edges 8E that form groove opening 8M, the distance from this line segment to bottom surface 8B is measured. The position where the distance from this line segment to bottom surface 8B is maximum is groove bottom 8T. The bottom surface 8B shown in Figure 2 is a curved surface. Bottom surface 8B may include a plane, and this plane may include groove bottom 8T. In this case, the width center of the plane is used as groove bottom 8T.

[0050] A groove 8 having a groove width WG of less than 1.0 mm at groove opening 8M is called a sipe. Grooves 8 other than sipes are also called normal grooves and have a groove width WG of 1.0 mm or more at their groove openings 8M. The sipe may include a portion having a groove width of 1.0 mm or more between the groove opening 8M and the groove bottom 8T (hereinafter, a portion corresponding to a normal groove). In this case, as the tread 4 wears and the portion corresponding to the normal groove is exposed, the sipe switches to a normal groove. The normal groove may include a portion having a groove width of less than 1.0 mm (a portion corresponding to a sipe) between the groove opening 8M and the groove bottom 8T. In this case, as the tread 4 wears and the portion corresponding to the sipe is exposed, the normal groove switches to a sipe. Even a normal groove that has a narrow groove width and allows the pair of groove walls 8W to contact each other when the tread 4 contacts the road surface is called a narrow groove. A normal groove that has a wide groove width and does not allow the pair of groove walls 8W to contact each other even when the tread 4 contacts the road surface is also called a main groove.

[0051] A plurality of circumferential grooves 10 are engraved in the tread 4. The plurality of circumferential grooves 10 each extend continuously in the circumferential direction. The circumferential grooves 10 are normal grooves and not siping grooves. Four circumferential grooves 10 are engraved in the tread 4 shown in FIG. 1. Of the four circumferential grooves 10, the two circumferential grooves 101 located on the outermost side in the axial direction are shoulder circumferential grooves. The two circumferential grooves 102 located on the inner side in the axial direction of the shoulder circumferential grooves 101 are middle circumferential grooves. This tread 4 includes two middle circumferential grooves 102 and two shoulder circumferential grooves 101. Five or more circumferential grooves 10 may be engraved in this tread 4.

[0052] The tread 4 includes a plurality of circumferential grooves 10. Thereby, a plurality of land portions 12 are formed. The plurality of land portions 12 are arranged in the axial direction. As described above, four circumferential grooves 10 are engraved in the tread 4 shown in FIG. 1. Five land portions 12 are formed in this tread 4. Of the five land portions 12, the two land portions 121 located on the outermost side in the axial direction are shoulder land portions. The two land portions 122 located on the inner side in the axial direction of the shoulder land portions 121 are middle land portions. The one land portion 123 located on the inner side in the axial direction of the middle land portions 122 is a center land portion. The tread 4 of this tire 2 includes one center land portion 123, two middle land portions 122, and two shoulder land portions 121.

[0053] When, for example, five circumferential grooves 10 are engraved in the tread 4, two center land portions 123 are formed on the axially inner side of the middle land portion 122. The circumferential groove 10 located between the two center land portions 123 is also called the center circumferential groove.

[0054] The circumferential groove 10 shown in FIG. 2 is the shoulder circumferential groove 101. The groove depth DGs of the shoulder circumferential groove 101 is, for example, 10 mm or more and 21 mm or less. From the viewpoint that the tire 2 can exhibit good wet performance, the groove depth DGs is preferably 13 mm or more and 18 mm or less. The ratio (WGs / TW) of the groove width WGs of the shoulder circumferential groove 101 to the width TW of the tread surface 6 is preferably 4.0% or more and 10% or less. As shown in FIG. 2, the shoulder circumferential groove 101 is configured such that its groove width gradually narrows from the groove opening 101M toward the groove bottom 101T.

[0055] Even when the tread 4 comes into contact with the road surface, the pair of groove walls 101W of the shoulder circumferential groove 101 do not contact each other. The shoulder circumferential groove 101 is a main groove. The shoulder circumferential groove 101 is also called the circumferential main groove 14. The plurality of circumferential grooves 10 engraved in the tread 4 of this tire 2 include a pair of circumferential main grooves 14.

[0056] FIG. 3 shows a cross section along line III-III of FIG. 1. FIG. 3 shows a part of the cross section of the tread 4. In this FIG. 3, the cross section of the center land portion 123 is shown. The circumferential groove 10 located between the center land portion 123 and the middle land portion 122 is the middle circumferential groove 102.

[0057] FIG. 4 shows a cross section of the middle circumferential groove 102. In this FIG. 4, the middle circumferential groove 102 on the second end TE2 side of the tread surface 6 is shown. The middle circumferential groove 102 has a pair of groove walls 102W that span between the groove opening 102M and the groove bottom 102T. Of the pair of groove walls 102W, the groove wall 102Wu on the equatorial plane side is the inner groove wall, and the groove wall 102Ws on the tread surface 6 end TE side is the outer groove wall. In the middle circumferential groove 102, the inner groove wall 102Wu and the outer groove wall 102Ws face each other. In FIG. 4, the length indicated by the double arrow DGh is the groove depth of the circumferential fine groove 20.

[0058] The middle circumferential groove 102 includes, as shape elements, a fine groove portion 16 and a widened portion 18. The fine groove portion 16 includes the groove opening 102M of the middle circumferential groove 102. The portion of the groove opening 102M may be processed in a tapered manner. In FIG. 4, the length indicated by the double arrow W1 is the minimum width of the fine groove portion 16. In the middle circumferential groove 102 shown in this FIG. 4, the fine groove portion 16 extends straight radially inward from the groove opening 102M. The fine groove portion 16 has a uniform groove width W1 as a whole. In FIG. 4, the dashed-dotted line NL is the center line of the minimum width of the fine groove portion 16. The fine groove portion 16 has a shape symmetric with respect to the minimum width center line NL.

[0059] The widened portion 18 is located radially inside the fine groove portion 16. The widened portion 18 includes the groove bottom 102T of the middle circumferential groove 102. The widened portion 18 has a shape asymmetric with respect to the minimum width center line NL. In FIG. 4, the position indicated by the symbol PU is the axial inner end of the widened portion 18. The position indicated by the symbol PS is the axial outer end of the widened portion 18. In FIG. 4, the length indicated by the double arrow W is the maximum width of the widened portion 18. The maximum width W is the distance from the axial inner end PU to the axial outer end PS of the widened portion 18. This maximum width W is measured along a line perpendicular to the minimum width center line NL. This maximum width W is represented by the sum of the shortest distance Wc from the minimum width center line NL to the axial inner end PU and the shortest distance Wm from the minimum width center line NL to the axial outer end PS. The portion of the middle circumferential groove 102 excluding the narrow groove portion 16, that is, the radially inner portion of the middle circumferential groove 102, tapers radially outward from the portion where the widened portion 18 exhibits the maximum width. The radially inner portion of the middle circumferential groove 102 tapers radially inward from the portion where the widened portion 18 exhibits the maximum width.

[0060] In this tire 2, the maximum width W of the widened portion 18 is wider than the minimum width W1 of the narrow groove portion 16. The groove width of the middle circumferential groove 102 exhibits the minimum width W1 in the narrow groove portion 16 and the maximum width W in the widened portion 18.

[0061] In this tire 2, when the tread 4 contacts the road surface and deforms, the opposing inner groove wall 102Wu and outer groove wall 102Ws of the middle circumferential groove 102 come into contact in the narrow groove portion 16. The middle circumferential groove 102 of this tire 2 is a narrow groove. This middle circumferential groove 102 is also called the circumferential narrow groove 20. As described above, the middle circumferential groove 102 includes the narrow groove portion 16 and the widened portion 18. Therefore, the circumferential narrow groove 20 includes the narrow groove portion 16 and the widened portion 18. When the tread 4 contacts the road surface and deforms, the opposing inner groove wall 102Wu and outer groove wall 102Ws of the circumferential narrow groove 20 come into contact in the narrow groove portion 16.

[0062] The plurality of circumferential grooves 10 engraved in the tread 4 include a pair of circumferential main grooves 14 and a pair of circumferential narrow grooves 20. The pair of circumferential narrow grooves 20 are respectively located axially inside the circumferential main grooves 14. The pair of circumferential narrow grooves 20 are located between the pair of circumferential main grooves 14.

[0063] As shown in FIG. 1, the center land portion 123 is located between the pair of circumferential narrow grooves 20. The center land portion 123 of this tire 2 is located on the equatorial plane. The middle land portion 122 is located between the circumferential narrow groove 20 and the circumferential main groove 14 located axially outside this circumferential narrow groove 20. The shoulder land portion 121 is located axially outside the circumferential main groove 14. The shoulder land portion 121 of this tire 2 includes the edge TE of the tread surface 6. The plurality of land portions 12 formed on the tread 4 include a center land portion 123, a pair of middle land portions 122, and a pair of shoulder land portions 121.

[0064] Between the pair of circumferential main grooves 14, three land portions 12 are located, specifically, a center land portion 123 and two middle land portions 122. On the three land portions 12 located between the pair of circumferential main grooves 14, a plurality of transverse sipes 22 crossing the land portions 12 are engraved. As a result, a plurality of blocks 24 are formed on the land portions 12. In each land portion 12, the plurality of blocks 24 are arranged in the circumferential direction.

[0065] As shown in FIG. 1, the shoulder land portion 121 located on the axially outer side of the circumferential main groove 14, that is, among the plurality of land portions 12 formed on the tread 4, the land portion 12 located on the outermost side in the axial direction, the transverse sipes 22 are not engraved. A plurality of transverse sipes 22 may be engraved on this shoulder land portion 121.

[0066] The transverse sipes 22 (hereinafter, center sipes 223) engraved on the center land portion 123 connect between the pair of circumferential fine grooves 20. In other words, the center land portion 123 has a plurality of center sipes 223 that connect between the pair of circumferential fine grooves 20. As a result, a plurality of blocks 24 (hereinafter, center blocks 243) are formed on the center land portion 123. The plurality of center blocks 243 are arranged in the circumferential direction.

[0067] The transverse sipes 22 (hereinafter, middle sipes 222) engraved on each middle land portion 122 connect between the circumferential fine groove 20 and the circumferential main groove 14. In other words, the middle land portion 122 has a plurality of middle sipes 222 that connect between the circumferential fine groove 20 and the circumferential main groove 14. As a result, a plurality of blocks 24 (hereinafter, middle blocks 242) are formed on the middle land portion 122. The plurality of middle blocks 242 are arranged in the circumferential direction.

[0068] The middle groove 222 is positioned circumferentially between one center groove 223 and another center groove 223 located adjacent to the one center groove 223. The center grooves 223 and the middle groove 222 are alternately arranged circumferentially.

[0069] FIG. 5 shows a cross section along the V-V line of FIG. 1. FIG. 5 shows a cross section of the center groove 223. The cross-sectional shape of the middle groove 222 is the same as that of the center groove 223. Taking the center groove 223 as an example, the cross-sectional shape of the transverse groove 22 is described.

[0070] The transverse groove 22 extends straight in its depth direction. The transverse groove 22 has a pair of wall surfaces 22W including the groove opening 22M and a bottom surface 22B including the groove bottom 22T. The length indicated by the double-headed arrow WGp in FIG. 5 is the groove width at the groove opening 22M of the transverse groove 22. The transverse groove 22 has a uniform groove width WGp from the groove opening 22M to the groove bottom 22T. The groove width WGp of the transverse groove 22 is less than 1.0 mm. When a load acts on the tread 4 and the tread 4 deforms, the wall surfaces 22W of the transverse groove 22 come into contact with each other and support each other. The length indicated by the double-headed arrow DGp is the groove depth of the transverse groove 22. The groove depth DGp of the transverse groove 22 is shallower than the groove depth D Gh of the circumferential fine groove 20. When the tread 4 wears, the transverse groove 22 disappears earlier than the circumferential fine groove 20.

[0071] Using FIG. 6, the manufacturing method of this tire 2 is described. In the manufacturing method of this tire 2, elements such as the tread 4 are molded, and these are combined to prepare a green tire 2r (a tire in an unvulcanized state) for the tire 2. The green tire 2r is put into the mold 26. The green tire 2r is pressurized and heated in the mold 26 to obtain the tire 2. The manufacturing method of this tire 2 includes a step of preparing the green tire 2r and a step of pressurizing and heating the green tire 2r in the mold 26. Pressurizing and heating the green tire 2r in the mold 26 is also called vulcanization molding, and the step of pressurizing and heating the green tire 2r is also called the vulcanization step. There are no particular restrictions on the vulcanization conditions such as temperature, pressure, and time for vulcanizing and molding the green tire 2r within the mold 26, and the vulcanization conditions set for conventional tires are adopted. As the mold 26, a mold that is common as a tire mold is used.

[0072] Although not described in detail, the mold 26 has a cavity surface 28 on its inner surface. The cavity surface 28 abuts against the outer surface of the green tire 2r and shapes the outer surface of the tire 2. This mold 26 is provided with a tread ring 30. The tread ring 30 is provided with a tread forming surface 32 on its inner surface. The tread forming surface 32 forms a part of the cavity surface 28. The tread forming surface 32 shapes the tread 4. This mold 26 is a split mold type. The tread ring 30 is provided with a plurality of segments 34 arranged in the circumferential direction. By combining these segments 34, the tread ring 30 is constituted.

[0073] Although not shown in the figure, the segment 34 is movable in the radial direction. When the vulcanization process is finished, the mold 26 is opened in order to release the tire 2 from the mold 26. At this time, the segment 34 moves radially outward. When the green tire 2r is loaded into the mold 26, the segment 34 moves radially inward. Thereby, the mold 26 is closed and the vulcanization process is started.

[0074] As described above, the tread 4 of this tire 2 has a plurality of circumferential grooves 10. The circumferential grooves 10 are shaped by ridges 38 that reflect their shape. The tread ring 30 is provided with ridges 38 corresponding to the circumferential grooves 10. The ridges 38 extend continuously in the circumferential direction. The ridges 38 protrude radially inward from a reference surface 32B of the tread forming surface 32. Although not described in detail, the reference surface 32B of the tread forming surface 32 corresponds to the aforementioned virtual tread surface. As described above, the plurality of circumferential grooves 10 include circumferential narrow grooves 20. The circumferential narrow grooves 20 are formed by ridges 38 (hereinafter, narrow ridges 40) that reflect the shape of the circumferential narrow grooves 20. Although not shown, the circumferential main grooves 14 are formed by thick ridges that reflect their shape.

[0075] The narrow ridge 40 has a bulging portion 42 at its tip. The bulging portion 42 corresponds to the widened portion 18 of the circumferential narrow groove 20. Although not described in detail, the narrow ridge 40 has a plate portion 44 corresponding to the narrow groove portion 16 of the circumferential narrow groove 20. The plate portion 44 is a plate-shaped member extending radially inward from the reference plane 32B. As described above, the circumferential narrow groove 20 shows a minimum width W1 in the narrow groove portion 16 and a maximum width W in the widened portion 18. Therefore, the narrow ridge 40 shows a minimum width in the plate portion 44 and a maximum width in the bulging portion 42.

[0076] As described above, transverse sipes 22 are engraved on the three land portions 12 located between the pair of circumferential main grooves 14. The transverse sipes 22 are formed by a blade 46. The transverse sipes 22 engraved on the center land portion 123, that is, the center sipes 223, span between the pair of circumferential narrow grooves 20. The blade 46 (hereinafter, center blade 463) for the center sipes 223 spans between the pair of narrow ridges 40. The transverse sipes 22 engraved on the middle land portion 122, that is, the middle sipes 222, span between the circumferential narrow groove 20 and the circumferential main groove 14. Although not shown, the blade 46 for the middle sipes 222 spans between the narrow ridge 40 and the ridge 38 for the circumferential main groove 14.

[0077] The tread 4 wears due to use. As a result, the grooves 8 gradually disappear. In the present invention, the stage from the new state until the groove portion 16 of the circumferential groove 20 disappears is the initial stage of wear. The stage from when the groove portion 16 disappears until the transverse rib 22 disappears is the intermediate stage of wear. The stage from when the transverse rib 22 disappears until the widened portion 18 of the circumferential groove 20, that is, until the circumferential groove 20 disappears, is the late stage of wear. When the circumferential groove 20 disappears is the timing to replace the tire 2.

[0078] In the initial stage of wear, when the tread 4 contacts the road surface and deforms, the opposing inner groove wall 102Wu and outer groove wall 102Ws of the circumferential groove 20 come into contact at the groove portion 16. Since the center land portion 123 and the middle land portion 122 support each other when the tread 4 contacts the road surface, the deformation of the tread 4 in the crown portion is suppressed. This tire 2 can reduce the rolling resistance. The groove volume of the circumferential groove 20 is smaller than the groove volume of the circumferential main groove 14. There is a concern that the wet performance of the tire 2 is more likely to be affected by the wear of the tread 4 compared to a conventional tread in which all of the circumferential grooves 10 provided in the tread 4 are constituted by the circumferential main groove 14. However, in the initial stage of wear, even if the tread 4 wears, the exposure of the transverse rib 22 continues. Since the transverse rib 22 can function as an edge component, this tire 2 can suppress the deterioration of wet performance. This tire 2 can suppress the deterioration of wet performance due to wear and achieve a reduction in rolling resistance in the initial stage of wear.

[0079] As described above, a transverse rib 22 that connects between the circumferential groove 20 and the circumferential main groove 14 is engraved on the middle land portion 122 of this tire 2. The transverse rib 22 engraved on this middle land portion 122 can also function as an edge component. Thereby, the deterioration of wet performance is effectively suppressed. From this viewpoint, it is preferable that the plurality of land portions 12 constituting the tread 4 have a middle land portion 122 located between the center land portion 123 and the shoulder land portion 121, and this middle land portion 122 has a transverse rib 22 that connects between the circumferential groove 20 and the circumferential main groove 14.

[0080] In the middle stage of wear, the groove portion 16 disappears, but the volume of the tread 4 decreases. Since the deformation of the tread 4 itself is suppressed, the tire 2 can maintain a low rolling resistance. Since the exposure of the transverse sipes 22 continues, the decrease in wet performance is suppressed. This tire 2 can suppress the decrease in wet performance due to wear and achieve a reduction in rolling resistance even in the middle stage of wear.

[0081] As described above, even when the tread 4 wears and the transverse sipes 22 disappear, the circumferential grooves 20 remain. Since the widened portion 18 is provided on the groove bottom 102T side of the circumferential grooves 20, the widened portion 18 is exposed in the late stage of wear. The exposed widened portion 18 can contribute to securing the groove volume. Even in the late stage of wear, the tire 2 can suppress the decrease in wet performance. In this late stage of wear, the volume of the tread 4 further decreases. Since the deformation of the tread 4 itself is suppressed, the tire 2 can maintain a low rolling resistance. This tire 2 can suppress the decrease in wet performance due to wear and achieve a reduction in rolling resistance even in the late stage of wear.

[0082] In the initial stage of wear, the deformation of the tread 4 is suppressed by the action of the groove portion 16 of the circumferential grooves 20. After the middle stage of wear, the deformation of the tread 4 is suppressed by the reduction of the volume of the tread 4. This tire 2 can maintain a low rolling resistance from the new state until the tire 2 needs to be replaced. From the initial stage to the middle stage of wear, the transverse sipes 22 can function as edge components. In the late stage of wear, the widened portion 18 can contribute to securing the groove volume. This tire 2 can maintain good wet performance from the new state until the tire 2 needs to be replaced. This tire 2 can suppress the decrease in wet performance due to wear and achieve a reduction in rolling resistance from the new state until the tire 2 needs to be replaced.

[0083] In the method for manufacturing the tire 2, when the vulcanization process is completed, the tire 2 is released from the mold 26. At this time, as described above, the segment 34 moves radially outward. As a result, the lug 38 and the blade 46 are pulled out from the tread 4. At this time, the bulging portion 42 of the fine lug 40 passes through the narrow groove portion 16 having a groove width narrower than that of the widened portion 18. The pulling out of the fine lug 40 is accompanied by deformation of the center land portion 123 and the middle land portion 122.

[0084] As described above, the center blade 463 bridges between the pair of fine lugs 40. In this mold 26, when pulling out the lug 38 and the blade 46 from the tread 4, for example, a part of the center land portion 123 may be caught at the connection portion between the center blade 463 and the fine lug 40.

[0085] In FIG. 6, the position indicated by the reference sign PUm is the axially inner end of the fine lug 40 (specifically, the bulging portion 42). The length indicated by the double-headed arrow WP is the distance between the pair of fine lugs 40 (hereinafter, the lug pitch). The lug pitch WP is narrower on the tip side of the fine lug 40 than on the reference plane 32B side. This lug pitch WP shows the minimum at the axially inner end PUm of the bulging portion 42. Therefore, when releasing the tire 2 from the mold 26, while the two fine lugs 40 press the center land portion 123 from both sides with their bulging portions 42, the lug 38 and the blade 46 are pulled out from the tread 4. There is a concern that high stress is generated in the center land portion 123 when pulling out the lug 38 and the blade 46 from the tread 4. Depending on the degree of stress generated in the center land portion 123, there is a risk of chipping in the center land portion 123.

[0086] However, in this tire 2, the widened portion 18 of the circumferential narrow groove 20 has an asymmetrical shape with respect to the minimum width center line NL of the narrow groove portion 16, and the maximum width center line WL of the widened portion 18 is located axially outside the minimum width center line NL of the narrow groove portion 16. In other words, the shortest distance Wc from the minimum width center line NL to the axially inner end PUm is shorter than the shortest distance Wm from the minimum width center line NL to the axially outer end PS. As a result, the tire 2 can reduce the amount of protrusion of the widened portion 18 inward in the axial direction while maintaining the maximum width W of the widened portion 18. When pulling out the lug 38 and the blade 46 from the tread 4, the force with which the bulging portions 42 of the two thin lugs 40 press against the center land portion 123 is reduced. Thereby, the increase in stress in the center land portion 123 is suppressed. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26. Since the widened portion 18 having a necessary groove volume is configured, even if the tread 4 wears and the transverse grooves 22 disappear, the exposed widened portion 18 can contribute to maintaining wet performance. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26, and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance.

[0087] As described above, the groove width of the shoulder circumferential groove 101 (that is, the circumferential main groove 14) gradually narrows from the groove opening 101M toward the groove bottom 101T. Therefore, the thick lug forming the circumferential main groove 14 tapers toward its tip. When pulling out the lug 38 and the blade 46 from the tread 4, the middle land portion 122 formed between the thin lug 40 and the thick lug can be deformed. In the middle land portion 122, an increase in stress that causes chipping is unlikely to occur.

[0088] The groove depth DGh of the circumferential thin groove 20 is the same as the groove depth DGs of the circumferential main groove 14, or the circumferential thin groove 20 is shallower than the circumferential main groove 14. As described above, the circumferential thin groove 20 has the widened portion 18 on the groove bottom 102T side. The widened portion 18 can effectively contribute to compensating for the reduced groove volume in the later stage of wear. This tire 2 can effectively suppress the deterioration of wet performance due to wear. From this perspective, it is preferable that the groove depth DGh of the circumferential thin groove 20 is the same as the groove depth DGs of the circumferential main groove 14, or the circumferential thin groove 20 is shallower than the circumferential main groove 14. In other words, the ratio (DGh / DGs) of the groove depth DGh of the circumferential thin groove 20 to the groove depth DGs of the circumferential main groove 14 is preferably 1.0 or less. In the latter stage of wear, from the viewpoint that the entire circumferential groove 20 can effectively contribute to compensating for the reduced groove volume of the widened portion 18 without disappearing, the ratio (DGh / DGs) is preferably 0.75 or more.

[0089] The minimum width W1 of the circumferential groove 20 is preferably 2.5 mm or less. In this case, the two land portions 12 located on both sides of the circumferential groove 20, specifically, the center land portion 123 and the middle land portion 122, support each other, and the deformation of these land portions 12 is effectively suppressed. This tire 2 can reduce the rolling resistance. From this viewpoint, the minimum width W1 is more preferably 2.0 mm or less.

[0090] The length indicated by the double arrow W2 in FIG. 7 is the axial distance from the outer groove wall 102Ws of the groove portion 16 at the position where the minimum width W1 is shown (hereinafter, the minimum width position) to the axial outer end PS of the widened portion 18. The length indicated by the double arrow W3 is the axial distance from the inner groove wall 102Wu of the groove portion 16 at the minimum width position to the axial inner end PU of the widened portion 18.

[0091] The axial distance W2 is longer than the minimum width W1 and longer than the axial distance W3. This tire 2 can suppress the amount of protrusion of the axially inner part of the widened portion 18 inward in the axial direction while maintaining the maximum width W of the widened portion 18. Since the widened portion 18 can contribute to securing the groove volume, even when the tread 4 wears and the transverse groove 22 disappears, the exposed widened portion 18 can contribute to maintaining the wet performance. When the fine rib 40 is pulled out from the tread 4, the force acting on the axially inner part of the widened portion 18 is effectively reduced, so the strain generated in the center land portion 123 is suppressed. The occurrence of tread chipping when the tire 2 is released from the mold 26 is suppressed. From this viewpoint, it is preferable that the axial distance W2 is longer than the minimum width W1 and longer than the axial distance W3.

[0092] The ratio W2 / W3 of the axial distance W2 to the axial distance W3 is preferably 1.5 or more and 4.0 or less. By setting the ratio W2 / W3 to 1.5 or more, this tire 2 can suppress the amount of protrusion of the axially inner portion of the widened portion 18 in the axially inward direction while maintaining the maximum width W of the widened portion 18. This tire 2 can maintain good wet performance while suppressing tread chipping. From this viewpoint, the ratio W2 / W3 is more preferably 1.7 or more. By setting the ratio W2 / W3 to 4.0 or less, this tire 2 can suppress the amount of protrusion of the axially outer portion of the widened portion 18 in the axially outward direction while maintaining the maximum width W of the widened portion 18. The influence of the axially outer portion of the widened portion 18 on the occurrence of chipping in the middle land portion 122 is effectively suppressed. Also in this case, this tire 2 can maintain good wet performance while suppressing tread chipping. From this viewpoint, the ratio W2 / W3 is more preferably 3.5 or less.

[0093] The circumferential groove 20 of this tire 2 can further have a bent portion 48 between the groove portion 16 and the widened portion 18. The bent portion 48 connects between the groove portion 16 and the widened portion 18. The groove width of the groove portion 16 is narrower than that of the widened portion 18. The distance between the groove walls in the bent portion 48 gradually widens from the groove portion 16 side toward the widened portion 18 side.

[0094] The position indicated by the reference numeral NC in FIG. 7 is the boundary between the groove portion 16 and the bent portion 48. This boundary NC is also called the first boundary for the purpose of distinguishing it from the boundary CW described later. The first boundary NC is also the inner end of the groove portion 16. The first boundary NC on the inner groove wall 102Wu is also called the inner first boundary NCu, and the first boundary NC on the outer groove wall 102Ws is also called the outer first boundary NCs. The position indicated by the reference numeral CW in FIG. 7 is the boundary between the bent portion 48 and the widened portion 18. This boundary CW is also called the second boundary for the purpose of distinguishing it from the aforementioned boundary NC. The second boundary CW on the inner groove wall 102Wu is also called the inner second boundary CWu, and the second boundary CW on the outer groove wall 102Ws is also called the outer second boundary CWs.

[0095] The portion from the inner first boundary NCu to the inner second boundary CWu in the inner groove wall 102Wu is the portion corresponding to the bent portion 48 in the inner groove wall 102Wu. The contour of the portion corresponding to the bent portion 48 in the inner groove wall 102Wu is represented by a single arc. In FIG. 7, the arrow R2 is the radius of the arc representing the contour of this portion. In the contour of the inner groove wall 102Wu, the arc representing the contour of the bent portion 48 is tangent to the line representing the contour of the fine groove portion 16 at the inner first boundary NCu. The arc representing the contour of this bent portion 48 is tangent to the line representing the contour of the widened portion 18 at the inner second boundary CWu.

[0096] In the contour of the inner groove wall 102Wu, the portion from the inner second boundary CWu to the groove bottom 102T is the portion corresponding to the widened portion 18. In this tire 2, the portion corresponding to this widened portion 18 is represented by a single arc. This portion may be represented by a plurality of arcs. As described above, the fine groove portion 16 extends straight. In the contour of the inner groove wall 102Wu, the contour of the portion corresponding to the fine groove portion 16 is represented by a straight line.

[0097] The portion from the outer first boundary NCs to the outer second boundary CWs in the outer groove wall 102Ws is the portion corresponding to the bent portion 48 in the outer groove wall 102Ws. The contour of the portion corresponding to the bent portion 48 in the outer groove wall 102Ws is represented by a single arc. In FIG. 7, the arrow R1 is the radius of the arc representing the contour of this portion. In the contour of the outer groove wall 102Ws, the arc representing the contour of the bent portion 48 is tangent to the line representing the contour of the fine groove portion 16 at the outer first boundary NCs. The arc representing the contour of this bent portion 48 is tangent to the line representing the contour of the widened portion 18 at the outer second boundary CWs.

[0098] In the contour of the outer groove wall 102Ws, the portion from the outer second boundary CWs to the groove bottom 102T is the portion corresponding to the widened portion 18. In this tire 2, the portion corresponding to this widened portion 18 is represented by a single arc. This portion may be represented by a plurality of arcs. As described above, the fine groove portion 16 extends straight. In the contour of the outer groove wall 102Ws, the contour of the portion corresponding to the fine groove portion 16 is represented by a straight line.

[0099] In this tire 2, an inner first boundary NCu, an outer first boundary NCs, an outer second boundary CWs, and an inner second boundary CWu are arranged in this order from the groove opening 102M toward the groove bottom 102T.

[0100] Thus, in this tire 2, the circumferential narrow groove 20 has a bent portion 48 between the narrow groove portion 16 and the widened portion 18, and the contour of the portion of the inner groove wall 102Wu corresponding to the bent portion 48 and the contour of the portion of the outer groove wall 102Ws corresponding to the bent portion 48 are represented by a single arc. This bent portion 48 can contribute to reducing the resistance when pulling out the thin rib 40 from the tread 4. Since the force acting on the widened portion 18 is effectively reduced, the strain generated in the center land portion 123 is suppressed. The occurrence of tread chipping when releasing the tire 2 from the mold 26 is suppressed. From this viewpoint, it is preferable that the circumferential narrow groove 20 has the bent portion 48 between the narrow groove portion 16 and the widened portion 18, and the contour of the portion of the inner groove wall 102Wu corresponding to the bent portion 48 and the contour of the portion of the outer groove wall 102Ws corresponding to the bent portion 48 are represented by a single arc.

[0101] The radius R2 of the arc representing the contour of the portion of the inner groove wall 102Wu corresponding to the bent portion 48 is larger than the radius R1 of the arc representing the contour of the portion of the outer groove wall 102Ws corresponding to the bent portion 48. Since the arc representing the contour of the portion of the inner groove wall 102Wu corresponding to the bent portion 48 has a large radius R2, the force acting on the axially inner portion of the widened portion 18 is effectively reduced when pulling out the thin rib 40 from the tread 4. Since the strain generated in the center land portion 123 is effectively suppressed, the occurrence of tread chipping when releasing the tire 2 from the mold 26 is suppressed. Since the arc representing the contour of the portion of the outer groove wall 102Ws corresponding to the bent portion 48 has a small radius R1, this tire 2 can secure the amount of protrusion axially outward of the axially outer portion of the widened portion 18. Since the widened portion 18 has a sufficient groove width and can contribute to securing the groove volume, even when the tread 4 wears and the transverse sipes 22 disappear, the exposed widened portion 18 can contribute to maintaining the wet performance.

[0102] The radius R1 of the arc representing the contour of the portion of the outer groove wall 102Ws corresponding to the bent portion 48 is 2.0 mm or more, and the ratio R2 / R1 of the radius R2 of the arc representing the contour of the portion of the inner groove wall 102Wu corresponding to the bent portion 48 to the radius R1 is preferably 2.0 or more. By setting the radius R1 to 2.0 mm or more, stress concentration at the bent portion 48 in the outer groove wall 102Ws is suppressed. Further, in this case, by setting the ratio R2 / R1 to 2.0 or more, the tire 2 can secure the amount of protrusion in the axial outward direction of the axially outer portion of the widened portion 18 while suppressing the amount of protrusion in the axial inward direction of the axially inner portion of the widened portion 18. This tire 2 can effectively suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26 and the deterioration of wet performance due to wear. From this viewpoint, the ratio R2 / R1 is more preferably 2.5 or more.

[0103] As shown in FIG. 3, in the radial direction, between the boundary NCu between the fine groove portion 16 and the bent portion 48 in the inner groove wall 102Wu and the axially inner end PU of the widened portion 18 located radially inside this boundary NCu, the transverse sipe 22 engraved on the center land portion 123, that is, the groove bottom 22T of the center sipe 223 is located. The center sipe 223 of this tire 2 has an appropriate groove depth DGp. The influence on the rigidity of the center land portion 123 by the center sipe 223 is effectively suppressed. Since the deformation of the tread 4 is effectively suppressed, this tire 2 can maintain a low rolling resistance from the state of being new until the tire 2 needs to be replaced. Since the center sipe 223 disappears at an appropriate timing, the widened portion 18 can fully exhibit its function. This tire 2 can maintain good wet performance from the state of being new until the tire 2 needs to be replaced. Since the connecting portion between the center blade 463 that forms the center sipe 223 and the fine convex strip 40 that forms the circumferential fine groove 20 has an appropriate length, when the convex strip 38 and the blade 46 are pulled out from the tread 4, the stress generated in the center land portion 123 is suppressed from increasing excessively. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26 and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance. From this perspective, in the radial direction, it is preferable that the transverse sipe 22 engraved on the center land portion 123, that is, the groove bottom 22T of the center sipe 223, is located between the boundary NCu between the fine groove portion 16 and the bent portion 48 on the inner groove wall 102Wu and the axial inner end PU of the widened portion 18 located radially inside this boundary NCu. From the same perspective, in the radial direction, it is more preferable that the groove bottom 22T of the center sipe 223 is located between the boundary NCs between the fine groove portion 16 and the bent portion 48 on the outer groove wall 102Ws and the axial outer end PS of the widened portion 18 located radially inside this boundary NCs. In the radial direction, it is even more preferable that the axial outer end PS of the widened portion 18 is located between the groove bottom 22T of the center sipe 223 and the axial inner end PU of the widened portion 18.

[0104] FIG. 8 shows a modified example of the circumferential fine groove 20. This FIG. 8 shows an example of the circumferential fine groove 20 in which the axial distance W3 from the inner groove wall 102Wu at the minimum width position of the fine groove portion 16 to the axial inner end PU of the widened portion 18 shown in FIG. 7 is set to 0 mm. This circumferential fine groove 20 also has a fine groove portion 16, a bent portion 48, and a widened portion 18.

[0105] In FIG. 8, the position indicated by reference sign PS is the axial outer end of the widened portion 18. In this circumferential groove 20, the widened portion 18 exhibits the maximum width W at the axial outer end PS. The position indicated by reference sign PUs is the position on the inner groove wall 102Wu where the widened portion 18 exhibits the maximum width W. In the circumferential groove 20 shown in this FIG. 8, the position PUs is the axial inner end of the widened portion 18. In FIG. 8, the straight line VL is a virtual straight line passing through the position on the inner groove wall 102Wu where the groove portion 16 exhibits the minimum width W1 and parallel to the minimum width center line NL of the groove portion 16. This virtual straight line VL includes the axial inner end PUs of the widened portion 18. In other words, the shortest distance from the minimum width center line NL to the axial inner end PUs of the widened portion 18 is equal to the shortest distance from the minimum width center line NL to the position on the inner groove wall 102Wu where the groove portion 16 exhibits the minimum width W1. The axial inner portion of the widened portion 18 does not protrude axially inward. When the fine rib 40 is pulled out from the tread 4, the strain generated in the axial inner portion of the widened portion 18 is minimized. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26. From this viewpoint, the circumferential groove 20 may be configured such that the virtual straight line VL including the inner groove wall 102Wu at the minimum width position of the groove portion 16 and parallel to the minimum width center line NL includes the axial inner end PUs of the widened portion 18. In this case, in this case, a widened portion 18 having a sufficient groove volume is configured, and even when the tread 4 wears and the transverse groove 22 disappears, from the viewpoint that the exposed widened portion 18 can contribute to maintaining the wet performance, the ratio W2 / W1 of the axial distance W2 from the outer groove wall 102Ws at the minimum width position of the groove portion 16 to the axial outer end PS of the widened portion 18 to the minimum width W1 of the groove portion 16 is preferably 2.0 or more, and more preferably 2.5 or more.

[0106] In FIG. 1, the angle θc is the angle formed by the length direction of the transverse groove 22, i.e., the center rib 223, i.e., the center land portion 123, with respect to the axial direction. This angle θc is preferably -35 degrees or more and 35 degrees or less. In this case, stress concentration at the corner of the center block 243, that is, at the portion where the center sip 223 joins the circumferential groove 20, is suppressed. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26. From this viewpoint, the angle θc is more preferably -25 degrees or more and 25 degrees or less.

[0107] In FIG. 1, the angle θm is the angle formed by the longitudinal direction of the transverse sip 22 engraved on the middle sip 222, that is, the middle land portion 122, with respect to the axial direction. This angle θm is preferably -35 degrees or more and 35 degrees or less. In this case, stress concentration at the corner of the middle block 242, that is, at the portion where the middle sip 222 joins the circumferential groove 20 or the circumferential main groove 14, is suppressed. This tire 2 can suppress the occurrence of tread chipping when releasing the tire 2 from the mold 26. From this viewpoint, the angle θm is more preferably -25 degrees or more and 25 degrees or less.

[0108] In FIG. 1, the double arrow L1 is the width of the middle land portion 122. The double arrow L2 is the width of the center land portion 123.

[0109] The ratio L2 / L1 of the width L2 of the center land portion 123 to the width L1 of the middle land portion 122 is preferably 0.5 or more and 2.0 or less. Thereby, both the center land portion 123 and the middle land portion 122 are configured with appropriate widths. Since each of the center land portion 123 and the middle land portion 122 has appropriate rigidity, the occurrence of tread chipping when releasing the tire 2 from the mold 26 is suppressed. From this viewpoint, the ratio L2 / L1 is more preferably 0.7 or more and 1.5 or less.

[0110] As is clear from the above description, according to the present invention, a heavy-duty tire 2 can be obtained that can suppress the occurrence of tread chipping when releasing from the mold and the deterioration of wet performance due to wear, and can achieve a reduction in rolling resistance.

Industrial Applicability

[0111] The technology described above, which can suppress the occurrence of tread chipping when releasing from the mold and the deterioration of wet performance due to wear and can achieve a reduction in rolling resistance, can be applied to various tires.

[0112] [Appendix] The present invention includes the following aspects.

[0113] [1] A tire including a tread, the tread having a tread surface that contacts the road surface, the tread including a plurality of circumferential grooves extending continuously in the circumferential direction, thereby forming a plurality of land portions arranged in the axial direction, the plurality of circumferential grooves including a pair of circumferential main grooves and a pair of circumferential fine grooves located between the pair of circumferential main grooves, the plurality of land portions including a center land portion located between the pair of circumferential fine grooves, a pair of middle land portions located between the circumferential fine groove and the circumferential main groove located outside the axial direction of the circumferential fine groove, and a pair of shoulder land portions located outside the axial direction of the circumferential main groove, the center land portion having a transverse siped connecting between the pair of circumferential fine grooves, each of the pair of circumferential fine grooves being deeper than the transverse siped, the circumferential fine groove including a groove portion and a widened portion located radially inside the groove portion, when the tread contacts the road surface and deforms, the opposing inner groove wall and outer groove wall of the circumferential fine groove contact in the groove portion, the maximum width W of the widened portion being wider than the minimum width W1 of the groove portion, the widened portion having an asymmetrical shape with respect to the center line of the minimum width of the groove portion, a heavy-duty tire in which the center line of the maximum width of the widened portion is located outside the axial direction of the center line of the minimum width of the groove portion. [2] The heavy-duty tire according to the above [1], wherein the minimum width W1 of the groove portion is 2.5 mm or less. [3] The axial distance W2 from the outer groove wall to the axial outer end of the widened portion at the minimum width position of the narrow groove portion is longer than the minimum width W1 of the narrow groove portion. The axial distance W2 is longer than the axial distance W3 from the inner groove wall to the axial inner end of the widened portion at the minimum width position of the narrow groove portion, and the heavy load tire according to the above [1] or [2]. [4] The circumferential narrow groove has a bent portion between the narrow groove portion and the widened portion. The contour of the portion of the inner groove wall corresponding to the bent portion and the contour of the portion of the outer groove wall corresponding to the bent portion are represented by a single arc, and the heavy load tire according to any one of the above [1] to [3]. [5] The radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion is larger than the radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion, and the heavy load tire according to the above [4]. [6] The angle formed by the transverse sipe with respect to the axial direction is -35 degrees or more and 35 degrees or less, and the heavy load tire according to any one of the above [1] to [5]. [7] The ratio L2 / L1 of the width L2 of the center land portion to the width L1 of the middle land portion is 0.5 or more and 2.0 or less, and the heavy load tire according to any one of the above [1] to [6]. [8] The ratio W2 / W3 of the axial distance W2 from the outer groove wall to the axial outer end of the widened portion at the minimum width position of the narrow groove portion to the axial distance W3 from the inner groove wall to the axial inner end of the widened portion at the minimum width position of the narrow groove portion is 1.5 or more and 4.0 or less, and the heavy load tire according to the above [3]. [9] The radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion is 2.0 mm or more. The ratio R2 / R1 of the radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion to the radius R1 is 2.0 or more, and the heavy load tire according to the above [4] or [5].

[10] The heavy-duty tire according to any one of [1] to [9] above, including the inner groove wall at the minimum width position of the narrow groove portion, and a virtual straight line parallel to the minimum width center line including the axial inner end of the widened portion.

[11] The heavy-duty tire according to

[10] above, wherein the ratio W2 / W1 of the axial distance W2 from the outer groove wall at the minimum width position of the narrow groove portion to the axial outer end of the widened portion to the minimum width W1 of the narrow groove portion is 2.0 or more.

[12] The heavy-duty tire according to [4], [5] or [9] above, wherein in the radial direction, the bottom of the transverse sipes is located between the boundary between the narrow groove portion and the bent portion on the inner groove wall and the axial inner end of the widened portion located radially inside the boundary.

Explanation of Signs

[0114] 2 ··· Tire 4 ··· Tread 6 ··· Tread surface 8 ··· Groove 10 ··· Circumferential groove 101 ··· Shoulder circumferential groove 102 ··· Middle circumferential groove 12 ··· Land 121 ··· Shoulder land 122 ··· Middle land 123 ··· Center land 14 ··· Circumferential main groove 16 ··· Narrow groove portion 18 ··· Widened portion 20 ··· Circumferential narrow groove 22 ··· Transverse sipes 223 ··· Center sipes 222 ··· Middle sipes 26 ··· Mold 28 ··· Cavity surface 30 ··· Tread ring 32 ··· Tread forming surface 34 ··· Segment 38 ··· Rib 40 ··· Narrow rib 42 ··· Bulge 44... Plate part 46... Blade 463... Center blade 48... Bending part

Claims

1. A tire comprising a tread, the tread having a tread surface that contacts the road surface, wherein the tread includes a plurality of circumferential grooves extending continuously in the circumferential direction, thereby forming a plurality of land portions arranged axially, the plurality of circumferential grooves include a pair of circumferential main grooves and a pair of circumferential fine grooves located between the pair of circumferential main grooves, the plurality of land portions include a center land portion located between the pair of circumferential fine grooves, a pair of middle land portions located between the circumferential fine grooves and the circumferential main grooves located axially outside the circumferential fine grooves, and a pair of shoulder land portions located axially outside the circumferential main grooves, the center land portion has a transverse sip connecting between the pair of circumferential fine grooves, each of the pair of circumferential fine grooves is deeper than the transverse sip, the circumferential fine groove includes a groove portion and a widened portion located radially inside the groove portion, when the tread contacts the road surface and deforms, the opposing inner groove wall and outer groove wall of the circumferential fine groove contact in the groove portion, the maximum width W of the widened portion is wider than the minimum width W1 of the groove portion, the widened portion has a shape asymmetric with respect to the minimum width center line of the groove portion, the maximum width center line of the widened portion is located axially outside the minimum width center line of the groove portion, A tire for heavy loads.

2. The minimum width W1 of the groove portion is 2.5 mm or less, The tire for heavy loads according to Claim 1.

3. The axial distance W2 from the outer groove wall at the minimum width position of the groove portion to the axial outer end of the widened portion is longer than the minimum width W1 of the groove portion, The axial distance W2 is longer than the axial distance W3 from the inner groove wall at the minimum width position of the groove portion to the axial inner end of the widened portion, The tire for heavy loads according to Claim 1.

4. The circumferential fine groove has a bent portion between the groove portion and the widened portion, The contour of the portion of the inner groove wall corresponding to the bent portion and the contour of the portion of the outer groove wall corresponding to the bent portion are represented by a single arc, The tire for heavy loads according to Claim 1.

5. The radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion is larger than the radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion, The tire for heavy loads according to Claim 4.

6. The angle formed by the transverse sip with respect to the axial direction is -35 degrees or more and 35 degrees or less, The heavy load tire according to claim 1.

7. The ratio L2 / L1 of the width L2 of the center land portion to the width L1 of the middle land portion is 0.5 or more and 2.0 or less. The heavy load tire according to claim 1.

8. The ratio W2 / W3 of the axial distance W2 from the outer groove wall to the axial outer end of the widened portion to the axial distance W3 from the inner groove wall to the axial inner end of the widened portion at the minimum width position of the narrow groove portion is 1.5 or more and 4.0 or less. The heavy load tire according to claim 3.

9. The radius R1 of the arc representing the contour of the portion of the outer groove wall corresponding to the bent portion is 2.0 mm or more. The ratio R2 / R1 of the radius R2 of the arc representing the contour of the portion of the inner groove wall corresponding to the bent portion to the radius R1 is 2.0 or more. The heavy load tire according to claim 4.

10. A virtual straight line parallel to the minimum width center line and including the inner groove wall at the minimum width position of the narrow groove portion includes the axial inner end of the widened portion. The heavy load tire according to claim 1.

11. The ratio W2 / W1 of the axial distance W2 from the outer groove wall to the axial outer end of the widened portion to the minimum width W1 of the narrow groove portion at the minimum width position of the narrow groove portion is 2.0 or more. The heavy load tire according to claim 10.

12. In the radial direction, the groove bottom of the transverse sipe is located between the boundary between the narrow groove portion and the bent portion on the inner groove wall and the axial inner end of the widened portion located radially inside the boundary. The heavy load tire according to claim 4.

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