Tire mold and method for manufacturing heavy-duty tire

Abstract

To provide a tire mold 104 capable of suppressing an occurrence of tread chipping and blade damage when releasing a tire having circumferential narrow grooves and lateral sipes that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear.SOLUTION: A mold 104 includes a tread ring 114. The tread ring 114 includes a pattern forming part 136. The pattern forming part 136 includes narrow groove ridges 144 and transverse blades 150. The tread ring 114 includes a plurality of dividing surfaces that traverse the pattern forming part 136. The plurality of dividing surfaces divide the tread ring 114 into a plurality of segments 120. The number of segments 120 included in the tread ring 114 is 17 or more.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a tire mold 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 tire mold and a method for manufacturing a heavy-duty tire that can contribute to the stable manufacture of tires having circumferential narrow grooves and lateral sipes that can suppress the occurrence of tread chipping and blade damage when releasing a tire, and that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. [Means for solving the problem]

[0008] The tire mold according to the present invention is a mold for forming a heavy-duty tire having a tread with a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves, the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion, the body portion including a narrow groove portion connected to the widened portion, and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion. The mold also 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 narrow groove ridges that protrude from a reference surface thereof and form the circumferential narrow grooves, and lateral blades that protrude from the reference surface and form the lateral sipes. The narrow groove ridges include a base portion that forms the body portion and a bulge portion that forms the widened portion. The base portion includes a plate-like portion that forms the narrow groove portion. The tread ring has a plurality of dividing surfaces that cross the pattern forming portion. The dividing surfaces divide the tread ring into a plurality of segments that are arranged in the circumferential direction. The number of segments included in the tread ring is 17 or more.

[0009] A method for manufacturing a heavy-duty tire according to the present invention is a method for manufacturing a heavy-duty tire comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves, the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion, the body portion including a narrow groove portion connected to the widened portion, and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion. The manufacturing method includes a step of pressurizing and heating a green tire for the tire in a mold, the mold being the tire mold described above. [Effects of the Invention]

[0010] The present invention can provide a tire mold and a method for manufacturing a heavy-duty tire that can contribute to the stable manufacture of tires with circumferential narrow grooves and lateral sipes that can suppress the occurrence of tread chipping and blade damage when releasing a tire, and that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. [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. 3 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 10 is a cross-sectional view showing a modified example of a horizontal sipe. [Figure 7] 1 is a cross-sectional view showing a part of a vulcanizer incorporating a tire mold, 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. 8 is a cross-sectional view showing a part of FIG. [Figure 13] FIG. 10 is a plan view showing the relationship between the pitch pattern and the division surface. [Figure 14] FIG. 10 is a development view showing a modified example of the dividing surface. [Figure 15] FIG. 10 is a cross-sectional view showing a modified example of a horizontal blade. 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. Sipes that cross the land area (hereinafter referred to as "transverse sipes") can function as edge components. By providing transverse sipes on the land area, the tire can suppress a decline in wet performance. By providing a widened portion with a groove width wider than the narrow groove portion on the groove bottom side of the circumferential narrow groove, the widened portion can contribute to ensuring groove volume. By exposing the widened portion, the tire can suppress a decrease in wet performance.

[0021] As described above, when circumferential narrow grooves are formed in the tread, the tread ring of the mold is provided with ridges that reflect the shape of the circumferential narrow grooves. When widened portions are provided in the circumferential narrow grooves, the shape of the widened portions is reflected in the tip portions of the ridges. When the tire is released from the mold after the vulcanization process is completed, the tip portions pass through the narrow grooves, which are narrower than the widened portions. Pulling out the ridges involves deformation of the land portions.

[0022] For example, when a transverse sipe is provided across a land portion sandwiched between two circumferential narrow grooves, the blade for the transverse sipe is connected to the ridge for the circumferential narrow groove. This mold has a connection between the ridge and the blade. When the tire is released from the mold, the rubber is likely to get caught at this connection. 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 connection part is located at the circumferential end of the segment, the stress acting on the land part is concentrated on the part that is in contact with the connection part, and depending on the extent of this, there is a concern that chips will occur in the land part, i.e., the tread, or that damage such as deformation or breakage will occur in the blades.

[0023] Therefore, the inventors have conducted extensive research into a tire mold that can suppress the occurrence of tread chipping and blade damage when a tire having circumferential narrow grooves and lateral sipes is released from the mold, 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 mold for forming a heavy-duty tire, the tire comprising a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves, the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion, the body portion including a narrow groove portion connected to the widened portion, and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion, the mold comprising a tread ring for forming the tread, the tread ring having a pattern forming portion for forming the tread pattern. the pattern forming portion comprises narrow groove ridges that protrude from its reference surface and form the circumferential narrow grooves, and horizontal blades that protrude from the reference surface and form the horizontal sipes, the narrow groove ridges have a base that forms the body portion and a bulge that forms the widened portion, the base has a plate-like portion that forms the narrow groove portion, the tread ring has a plurality of dividing surfaces that cross the pattern forming portion, and the plurality of dividing surfaces divide the tread ring into a plurality of segments that are aligned in the circumferential direction, and the number of the segments included in the tread ring is 17 or more.

[0025] The tire mold of the present invention can suppress the occurrence of tread chipping and blade damage when releasing a tire, and can contribute to the stable production of tires with circumferential narrow grooves and lateral sipes that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. The mechanism by which these effects are achieved has not been clarified, but is presumed to be as follows.

[0026] In tires manufactured using this mold, the tread comes into contact with the road surface and deforms, causing a pair of wall surfaces of the circumferential narrow groove to come into contact with each other at the narrow groove portion. The two land portions arranged on either side of the circumferential narrow groove support each other, suppressing deformation of the land portions. This tire can reduce rolling resistance. The lateral sipes can function as edge components, allowing the tire to maintain good wet performance even as the tread wears. The widened portions provided on the bottom side of the circumferential narrow grooves contribute to ensuring groove volume. Even if the lateral sipes disappear due to tread wear, the exposed widened portions 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 achieve reduced rolling resistance.

[0027] The tread ring of the mold for this tire has narrow groove ridges that form circumferential narrow grooves and lateral blades that form lateral sipes. In the tire, the lateral sipes are connected to the circumferential narrow grooves. The tread ring has a connecting portion between the narrow groove ridges and the lateral blades (hereinafter referred to as the ridge-blade connecting portion).

[0028] The tread ring has multiple segments arranged circumferentially. The mold is a split mold. The deviation of the protruding direction of the narrow grooves and transverse blades relative to the pulling direction is greatest at the circumferential ends of the segments. In other words, when the tire is released from the mold, the closer to the circumferential ends of the segments, the more the narrow grooves and transverse blades are pulled out at an angle relative to their protruding direction. When the tire is released from the mold, stress acting on the land portion is concentrated near the connection points of the protruding blades, and depending on the extent of this, there is a concern that tread chipping or blade damage may occur.

[0029] In a conventional mold, the number of segments constituting the 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 a conventional mold, the angle representing the deviation of the protruding direction of the narrow groove ridges and transverse blades from the drawing direction is maximum at the circumferential end of the segment, and is 18.0 to 22.5 degrees. In contrast, in the mold of the present invention, the number of segments constituting the tread ring is 17 or more. In the mold of the present invention, the angle representing the deviation of the protruding direction from the drawing direction is 10.6 degrees or less. By setting the number of segments to 17 or more, this mold can reduce the deviation of the protruding direction from the drawing direction. This mold can reduce stress concentration that occurs near the connection portion of the ridges and blades due to this deviation. This mold can suppress the occurrence of tread chipping and blade damage when releasing the tire.

[0030] This tire mold can suppress the occurrence of tread chipping and blade damage when releasing the tire, and can contribute to the stable production of tires with circumferential narrow grooves and lateral sipes that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear.

[0031] Preferably, in the cross-sectional outline of the narrow groove ridge along a plane perpendicular to the longitudinal direction of the narrow groove ridge, the portion transitioning from the plate-like portion to the bulge portion is an inner transition portion, the inner transition portion is represented by an arc having a radius R1, the minimum width W1 of the plate-like portion is narrower than the maximum width W2 of the bulge portion, and the radius R1 of the arc representing the inner transition portion is greater than half the maximum width W2 of the bulge portion. In this case, this mold can suppress the occurrence of tread chipping and blade damage when the tire is released.

[0032] Preferably, the ratio W1 / W2 of the minimum width W1 of the plate-like portion to the maximum width W2 of the bulge portion is 0.10 or more and 0.35 or less. In this case, this mold can suppress the occurrence of tread chipping and blade damage when the tire is released. Tires manufactured with this mold can suppress deterioration of wet performance due to wear.

[0033] Preferably, the minimum width W1 of the plate-like portion is 2.5 mm or less, in which case the rolling resistance of a tire manufactured using this mold can be reduced.

[0034] Preferably, the body of the circumferential narrow groove has a funnel portion located radially outward of the narrow groove portion, the base has a tapered portion forming the funnel portion, the portion in the cross-sectional outline of the narrow groove ridge where the plate-like portion transitions to the tapered portion is an outer transition portion, the outer transition portion is represented by an arc having a radius R2, and the ratio R1 / R2 of the radius R1 of the arc representing the inner transition portion to the radius R2 of the arc representing the outer transition portion is 1.5 or more. In this case, this mold can suppress the occurrence of tread chipping and blade damage when releasing the tire.

[0035] Preferably, the ratio D2 / D1 of the protruding length D2 of the base to the protruding length D1 of the narrow groove ridge is 0.25 or more and 0.70 or less. In this case, this mold can suppress the occurrence of tread chipping and blade damage when the tire is released. Tires manufactured with this mold can reduce rolling resistance.

[0036] Preferably, the protruding length D2 of the base portion, the protruding length D3 from the reference plane to the position indicating the maximum width W1 of the bulging portion, and the protruding length D5 of the horizontal blade satisfy the following formula. Formula: D2≦D5≦D3 In this case, this mold can suppress the occurrence of tread chipping and blade damage when releasing the tire. Tires manufactured with this mold can suppress the deterioration of wet performance due to wear and can reduce rolling resistance.

[0037] Preferably, the angle formed by the lateral blade with respect to the axial direction is equal to or greater than -35 degrees and equal to or less than 35 degrees. In this case, the mold can suppress the occurrence of tread chipping and blade damage when the tire is released.

[0038] Preferably, the lateral blades extend in a zigzag pattern in the protruding direction and in the length direction, in which case the rolling resistance of a tire manufactured using this mold can be reduced.

[0039] Preferably, the thickness of the lateral blade is 0.4 mm or more and 0.7 mm or less. In this case, this mold can suppress the occurrence of blade damage when releasing the tire. Tires manufactured with this mold can reduce rolling resistance.

[0040] Preferably, the shortest distance from the lateral blade closest to the dividing surface to the dividing surface is shorter than the radius R1 of the arc representing the inner transition portion. In this case, this mold can suppress the occurrence of tread chipping and blade damage when the tire is released.

[0041] 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.

[0042] Preferably, the protrusion length D6 of the lateral blade at the end of the lateral blade is shorter than the protrusion length D7 of the lateral blade at the center of the lateral blade. In this case, even if the tip of the center of the lateral blade is positioned near the maximum width position of the bulging portion of the narrow groove ridge, the protrusion length D6 of the end connected to the narrow groove ridge is short, thereby preventing the rubber from getting caught at the ridge-blade connection portion when the narrow groove ridge and the lateral blade are pulled out of the tread. This mold can reduce stress concentration near the connection portion. Even if the tip of the center of the lateral blade is positioned near the maximum width position of the bulging portion of the narrow groove ridge, this mold can prevent tread chipping and blade damage when releasing the tire. By positioning the tip of the center of the lateral blade near the maximum width position of the bulging portion of the narrow groove ridge, this mold can provide the tire with lateral sipes that function as edge components until the final stage of wear when the tire needs to be replaced. In this case, the tire can maintain good wet performance from a new state until the tire needs to be replaced.

[0043] Preferably, the protruding length D2 of the base, the protruding length D3 from the reference plane to the position indicating the maximum width W2 of the bulge, and the protruding length D6 of the horizontal blade at the end of the horizontal blade satisfy the following formula: Formula: D2≦D6≦D3 In this case, this mold can suppress the occurrence of tread chipping and blade damage when releasing the tire. Tires manufactured with this mold can suppress the deterioration of wet performance due to wear and can reduce rolling resistance.

[0044] The present invention provides a method for manufacturing a heavy-duty tire, the method comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves; a body portion and a widened portion located radially inward of the body portion; a narrow groove portion connected to the widened portion; and when the tread contacts a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion. The method includes a step of pressurizing and heating a green tire for the tire in a mold, the mold being the tire mold described above. This manufacturing method can reduce the occurrence of tread chipping and blade damage when the tire is released. Tires manufactured by this manufacturing method can reduce rolling resistance and reduce deterioration of wet performance due to wear.

[0045] As described above, the tire mold and heavy-duty tire manufacturing method of the present invention can suppress the occurrence of tread chipping and blade damage when releasing the tire, and can contribute to the stable manufacturing of tires with circumferential narrow grooves and lateral sipes that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. This will be explained in detail below using the heavy-duty tire shown in Figure 1 as an example.

[0046] [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.

[0047] 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.

[0048] The tire 2 has a tread 4. The tread 4 is made of cross-linked 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 is 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.

[0049] 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.

[0050] 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.

[0051] Grooves 8 are cut into the tread 4. This forms a tread pattern. The tread 4 of this tire 2 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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. Even among ordinary grooves, those with a narrow groove width and a pair of wall surfaces that can 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 and a pair of wall surfaces that do not come into contact with each other when the tread comes into contact with the road surface and deforms are also called main grooves.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] The shoulder circumferential groove 12 of this tire 2 includes an outer vertex 12s close to the edge TE of the tread surface 6 and an inner vertex 12u close to the equatorial plane. The outer vertices 12s and the inner vertices 12u are arranged alternately in the circumferential direction. The shoulder circumferential groove 12 extends circumferentially, alternately passing through the outer vertices 12s and the inner vertices 12u. The shoulder circumferential groove 12 extends in a zigzag manner in the circumferential direction. The shoulder circumferential groove 12 may also extend straight in the circumferential direction.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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 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.

[0077] The center land portion 24 is located between two center circumferential grooves 14. The middle land portion 26 is located between the center circumferential groove 14 and the shoulder circumferential groove 12. The center land portion 24 and the middle land portion 26 are each a land portion 20 between adjacent circumferential grooves 10. In the present invention, among the plurality of land portions formed in the tread, the land portion between adjacent circumferential grooves is also called a main land portion.

[0078] The center land portion 24 and the middle land portion 26 are main land portions 28. The five land portions 20 formed in the tread 4 include three main land portions 28 located between adjacent circumferential grooves 10. The tread 4 of this tire 2 is formed with a plurality of land portions 20 aligned in the axial direction, and the plurality of land portions 20 includes a plurality of main land portions 28 located between adjacent circumferential grooves 10.

[0079] In the present invention, among the plurality of main land portions, the main land portion located on the outermost side in the axial direction is also referred to as an outer main land portion, and the main land portion located between the left and right outer main land portions is also referred to as an inner main land portion. In this tire 2, of the main land portions 28, that is, the center land portion 24 and the pair of middle land portions 26, the main land portion 28 located axially outermost is the middle land portion 26. The middle land portion 26 is the outer main land portion 28s. The center land portion 24 is the inner main land portion 28u.

[0080] The shoulder circumferential groove 12 is located axially outward of the middle land portion 26. As described above, the shoulder circumferential groove 12 is the circumferential main groove 16. The circumferential groove 10 located axially outward of the outer main land portion 28s is the circumferential main groove 16 having a groove width wider than the groove width of the circumferential narrow groove 18.

[0081] The shoulder land portion 22 is located axially outward of the shoulder circumferential groove 12 and includes the edge TE of the tread surface 6. The shoulder land portion 22 is located further outward of the shoulder circumferential groove 12 located axially outermost. The shoulder land portion 22 is not a main land portion 28.

[0082] In this tire 2, a land portion 20 may be further provided between the shoulder land portion 22 and the middle land portion 26. In this case, the land portion 20 located between the shoulder land portion 22 and the middle land portion 26 has circumferential grooves 10 located on both sides thereof, and therefore is a main land portion 28. A plurality of land portions 20 may be further provided between the shoulder land portion 22 and the middle land portion 26.

[0083] In this tire 2, a plurality of lateral grooves 30 are formed in all land portions 20 formed in the tread 4, crossing the land portions 20. As a result, a plurality of blocks 32 arranged in the circumferential direction are formed in each land portion 20. The tread pattern of this tire 2 is a block pattern.

[0084] The lateral grooves 30 formed in the center land portion 24 bridge between the inner narrow groove 52 of the first center circumferential groove 14a and the inner narrow groove 52 of the second center circumferential groove 14b. The lateral grooves 30 formed in the first middle land portion 26a bridge between the inner apex 12u of the first shoulder circumferential groove 12a and the outer narrow groove 50 of the first center circumferential groove 14a. The lateral grooves 30 formed in the second middle land portion 26b bridge between the inner apex 12u of the second shoulder circumferential groove 12b and the outer narrow groove 50 of the second center circumferential groove 14b.

[0085] Although not described in detail, the lateral grooves 30 are constituted by only a lateral groove body 34 as a normal groove, or by a composite of the lateral groove body 34 and a lateral groove sipe 36 as a sipe. When the lateral grooves 30 have the lateral groove body 34 and the lateral groove sipe 36, the lateral groove sipe 36 is cut into the bottom surface of the lateral groove body 34.

[0086] The lateral grooves 30 cut into the main land portion 28 are entirely composed of a composite of a lateral groove body 34 and a lateral groove sipe 36. The lateral grooves 30 include a lateral groove body 34 and a lateral groove sipe 36 located radially inward of the lateral groove body 34. The lateral groove body 34 and the lateral groove sipe 36 bridge between two circumferential grooves 10 arranged so as to sandwich the main land portion 28 therebetween. The groove depth of the lateral grooves 30 formed in the main land portion 28 is slightly shallower than the groove depth DGs of the shoulder circumferential grooves 12. Specifically, the groove depth of the lateral grooves 30 is preferably set in the range of 0.85 to 0.95 times the groove depth DGs of the shoulder circumferential grooves 12.

[0087] The lateral grooves 30 cut in the shoulder land portion 22 include an inner portion 38 that connects to the shoulder circumferential groove 12, and an outer portion 40 that is located axially outward of the inner portion 38. The entire inner portion 38 is composed of only the lateral groove body 34. Similar to the lateral grooves 30 cut in the main land portion 28, the outer portion 40 is composed of a composite of the lateral groove body 34 and the lateral groove sipes 36. The lateral groove body 34 of the outer portion 40 is shallower than the lateral groove body 34 of the inner portion 38. The lateral grooves 30 formed in the shoulder land portions 22 have a groove depth that is approximately the same as the groove depth of the lateral grooves 30 formed in the main land portions 28. The lateral grooves 30 formed in the shoulder land portions 22 have a groove width that is approximately the same as the groove width WGy of the lateral grooves 30 formed in the main land portions 28. The shoulder narrow grooves 42, which are the narrow grooves described above, are formed in the blocks 32 that are formed in the shoulder land portions 22. The shoulder narrow grooves 42 connect the inner portion 38 on the leading side and the outer portion 40 on the trailing side.

[0088] Fig. 4 shows a cross section of the center circumferential groove 14 taken along line IV-IV in Fig. 2. As described above, the center circumferential groove 14 is a circumferential narrow groove 18. Fig. 4 shows a cross section of the circumferential narrow groove 18.

[0089] The circumferential narrow groove 18 includes a body portion 54 and a widened portion 56. 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 widened portion 56 is located radially inward of the body portion 54. When the tread 4 wears and the body portion 54 disappears, the widened portion 56 becomes exposed.

[0090] The body portion 54 of this tire 2 includes a funnel portion 58 and a narrow groove portion 60. A groove opening 18M of this circumferential narrow groove 18 is processed to have a tapered shape.

[0091] The funnel portion 58 is located radially outward of the narrow groove portion 60. The funnel portion 58 includes the groove mouth 18M of the circumferential narrow groove 18. The funnel portion 58 tapers inward from the groove mouth 18M. The outline of the wall surface of the funnel portion 58 shown in FIG. 4 is represented by a straight line. This outline may also be represented by a curved line. 4 is the groove width at the groove mouth 18M of the funnel portion 58. The groove width WA of the funnel portion 58 is preferably 0.15 to 0.45 times the groove width WGs of the shoulder circumferential groove 12.

[0092] The narrow groove portion 60 is located radially inside the funnel portion 58. The narrow groove portion 60 is continuous with the funnel portion 58. The narrow groove portion 60 extends straight in the depth direction of the circumferential narrow groove 18. In the cross section shown in FIG. 4, the contour of the wall surface of the narrow groove portion 60 is represented by a straight line. The length indicated by the double arrow W1t in FIG. 4 is the minimum width of the narrow groove portion 60. The narrow groove portion 60 has a uniform groove width W1t in the depth direction of the circumferential narrow groove 18. 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 of the tire 2 is expressed as the groove width W1t of the narrow groove portion 60. The groove width W1t of the narrow groove portion 60 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 60 when the tread 4 comes into contact with the road surface and deforms.

[0093] The widened portion 56 is located radially inward of the narrow groove portion 60. The widened portion 56 is continuous with the narrow groove portion 60. In other words, the narrow groove portion 60 of the body portion 54 is connected to the widened portion 56. The widened portion 56 has a groove width wider than the minimum width W1t of the narrow groove portion 60. 4, the length indicated by the double-headed arrow W2t is the maximum width of the widened portion 56. The position indicated by the symbol PX is the position where the widened portion 56 has the maximum width W2t (hereinafter referred to as the maximum width position PX). The portion of the circumferential narrow groove 18 excluding the body portion 54, i.e., the widened portion 56 of the circumferential narrow groove 18, tapers outward from the maximum width position PX and tapers inward from the maximum width position PX.

[0094] The length indicated by the double-headed arrow D1t in FIG. The groove depth D1t 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 D1t / DGs of the groove depth D1t of the circumferential narrow groove 18 to the shoulder circumferential groove DGs is 0.75 or more and 1.00 or less.

[0095] As described above, the land portion 20 of the tire 2 is configured with a plurality of blocks 32. The main land portion 28 of the tire 2 has a plurality of blocks 32 arranged in the circumferential direction. A lateral sipe 62 is formed in each block 32 of the main land portion 28. Each block 32 formed in the main land portion 28 (hereinafter referred to as a main block 32) has the lateral sipe 62. The lateral sipes 62 provided in the blocks 32 (hereinafter referred to as first outer main blocks) constituting the outer main land portion 28s located on the first end TE1 side of the tread surface 6 bridge between the vicinity of the inner apex 12u of the first circumferential main groove 16a and the inner narrow groove 52 of the first circumferential narrow groove 18a. The lateral sipes 62 provided in the blocks 32 (hereinafter referred to as second outer main blocks) constituting the outer main land portion 28s located on the second end TE2 side bridge between the vicinity of the inner apex 12u of the second circumferential main groove 16b and the inner narrow groove 52 of the second circumferential narrow groove 18b. The lateral sipes 62 provided in the blocks 32 (hereinafter referred to as inner main blocks 32) constituting the inner main land portion 28u bridge between the outer narrow grooves 50 of the first circumferential narrow grooves 18a and the outer narrow grooves 50 of the second circumferential narrow grooves 18b.

[0096] The lateral sipes 62 provided in each main block 32 bridge between two circumferential grooves 10 arranged on either side of the block 32. The lateral sipes 62 are transverse sipes that cross the block 32. One end of the lateral sipe 62 may remain within the block 32, and the other end of the lateral sipe 62 may be connected to the circumferential groove 10. In this case, the block 32 is connected to one circumferential groove 10.

[0097] 5 shows a cross section of the lateral sipe 62 taken along line VV in FIG. 2. The cross section of the lateral sipe 62 shown in FIG. 5 is a cross section of the lateral sipe 62 provided in the inner main block 32. As described above, the lateral sipe 62 is also provided in the block 32 of the outer main land portion 28s (hereinafter referred to as the outer main block 32). The cross-sectional shape of this lateral sipe 62 is the same as the cross-sectional shape of the lateral sipe 62 provided in the inner main block 32. A description of the cross-sectional shape of the lateral sipe 62 provided in the outer main block 32 will be omitted.

[0098] The lateral sipes 62 are the sipes described above. The groove width Wp of the lateral sipes 62 at the groove opening 62M is less than 1.0 mm. The lateral sipes 62 extend in a zigzag pattern in their length and depth directions. The lateral sipes 62 are three-dimensional sipes. As shown in FIG. 6, the lateral sipes 62 may be two-dimensional sipes that extend like a flat plate. In this case, the lateral sipes 62 extend straight in their length and depth directions. Although not shown, the lateral sipes 62 may have a tubular portion with a wide groove width on the groove bottom 62T side. In this case, the lateral sipes 62 have a sipe main body that functions as a sipe and a tubular portion located radially inside the sipe main body.

[0099] The length indicated by the double arrow DA in FIG. The lateral sipes 62 of this tire 2 are shallower than the circumferential narrow grooves 18. Specifically, the ratio DA / D1t of the groove depth DA of the lateral sipes 62 to the groove depth D1t of the circumferential narrow grooves 18 is equal to or greater than 0.80 and equal to or less than 1.00.

[0100] Circumferential narrow grooves 18 and lateral sipes 62 are formed in the tread 4 of the tire 2. For example, as shown in FIG. 2, the lateral sipes 62 are connected to the circumferential narrow grooves 18. The tread 4 has a tread pattern including the circumferential narrow grooves 18 and the lateral sipes 62 connected to the circumferential narrow grooves 18. As described above, the circumferential narrow grooves 18 include a body portion 54 and an expanded portion 56 located radially inward of the body portion 54, and the body portion 54 includes a narrow groove portion 60 connected to the expanded portion 56. 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 60. A tire 2 having such a tread pattern is manufactured as follows.

[0101] [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.

[0102] [Vulcanizer] A vulcanizer is used in the vulcanization process. An overview of the vulcanizer will be described below, and for the sake of convenience, the configuration of the vulcanizer and the mold set in this vulcanizer will be expressed using the dimensions of a tire.

[0103] A tire mold 104 according to one embodiment of the present invention 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.

[0104] 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.

[0105] 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.

[0106] [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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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, i.e., 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 .

[0111] 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.

[0112] 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 upper holding plate 132 is then raised, causing the upper side plate 116 and bead ring 118 to move upward. The actuator 130 is then 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 30, shoulder narrow grooves 42, and lateral sipes 62. 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 30, narrow groove plates 148 that form the shoulder narrow grooves 42, and lateral blades 150 that form the lateral sipes 62.

[0117] 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. The dashed line CH is the width center line of the narrow groove ridge 144. The cross section of the narrow groove ridge 144 shown in Fig. 10 has a shape symmetrical with respect to the width center line CH.

[0118] 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 ridges 144 protrude from the reference plane BL. The direction of the width center line CH is the protruding direction of the narrow groove ridges 144. The protruding direction of the narrow groove ridges 144 corresponds to the depth direction of the circumferential narrow grooves 18. The position indicated by the symbol PHT is the tip of the narrow groove ridge 144. The tip PHT corresponds to the groove bottom 18T of the circumferential narrow groove 18. The width center line CH passes through the tip PHT.

[0119] The dotted line LS indicates the overlapping portion between the narrow groove ridge 144 and the reference plane BL. The position indicated by the symbol PHE is the end of the overlapping portion LS. The position PHE corresponds to the edge 18E that forms the groove opening 18M of the circumferential narrow groove 18. The position PHE is also called the edge corresponding position.

[0120] The narrow groove ridge 144 has a base portion 152 and a bulge portion 154. The base portion 152 forms the body portion 54 of the circumferential narrow groove 18. The bulge portion 154 forms the widened portion 56 of the circumferential narrow groove 18.

[0121] The base 152 includes a tapered portion 156 and a plate-shaped portion 158. The tapered portion 156 forms the funnel portion 58 of the circumferential narrow groove 18. The plate-shaped portion 158 forms the narrow groove portion 60 of the circumferential narrow groove 18. When the funnel portion 58 is not provided in the circumferential narrow groove 18, the base 152 is composed of only the plate-shaped portion 158.

[0122] The tapered portion 156 includes an edge corresponding position PHE. The tapered portion 156 tapers inward. The width of the tapered portion 156 is wider than the width of the plate-shaped portion 158. The plate-shaped portion 158 is located radially inside the tapered portion 156. The plate-shaped portion 158 is continuous with the tapered portion 156. The length indicated by the double-headed arrow W1 is the minimum width of the plate-shaped portion 158. The plate-shaped portion 158 of this narrow groove ridge 144 extends straight in the protruding direction. The plate-shaped portion 158 has a uniform width W1.

[0123] The bulging portion 154 is located radially inward of the base portion 152. The bulging portion 154 is continuous with the plate-like portion 158 of the base portion 152. The bulging portion 154 includes the tip end PHT of the narrow groove ridge 144. The length indicated by the double-headed arrow W2 is the maximum width of the bulge portion 154. The position indicated by the symbol PXm is the position where the bulge portion 154 has the maximum width W2 (hereinafter referred to as the maximum width position PXm). The bulge portion 154 tapers from the maximum width position PXm toward the plate-shaped portion 158, and tapers from the maximum width position PXm toward the tip PHT. The maximum width W2 of the bulge portion 154 is wider than the minimum width W1 of the plate-shaped portion 158. The width of the bulge portion 154 is wider than the width of the plate-shaped portion 158.

[0124] The position indicated by the solid line LTP is the boundary between the tapered portion 156 and the plate-like portion 158. This boundary LTP is represented by the position at the boundary between the tapered portion 156 and the plate-like portion 158 where the narrow groove ridge 144 exhibits a width Wa that is 1.1 times the minimum width W1 of the plate-like portion 158. When the portion that exhibits the width Wa that is 1.1 times the minimum width W1 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 plate-shaped portion 158 and the bulging portion 154. This boundary LPE is represented by the position at the boundary between the plate-shaped portion 158 and the bulging portion 154 where the narrow groove ridge 144 exhibits a width Wb that is 1.1 times the minimum width W1 of the plate-shaped portion 158. When the portion that exhibits the width Wb that is 1.1 times the minimum width W1 has a certain length, the radially outer end of that portion is used as the boundary LTP.

[0125] 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 62 shown in Figure 5.

[0126] The horizontal blade 150 protrudes from the reference plane BL of the pattern forming portion 136 . As described above, the lateral sipes 62 extend in a zigzag pattern in their length and depth directions. The lateral blades 150 extend in a zigzag pattern in their length and protrusion directions. The lateral blades 150 are three-dimensional blades. When the lateral sipes 62 are two-dimensional sipes as shown in FIG. 6, the lateral blades 150 are also flat blades (also called two-dimensional blades). In this case, the lateral blades 150 extend straight in their length and protrusion directions.

[0127] In the tire 2 manufactured using this mold 104, the tread 4 comes into contact with the road surface and deforms, causing a pair of wall surfaces 18S of the circumferential narrow groove 18 to come into contact with each other at the narrow groove portion 60. The two main land portions 28 arranged on either side of the circumferential narrow groove 18 support each other, suppressing deformation of the main land portions 28. This tire 2 can reduce rolling resistance. The lateral sipes 62 can function as edge components. The tire 2 can maintain good wet performance even when the tread 4 is worn. The widened portion 56 provided on the groove bottom 18T side of the circumferential narrow groove 18 can contribute to ensuring groove volume. Even if the tread 4 wears and the lateral sipes 62 disappear, the exposed widened portion 56 can contribute to maintaining wet performance. This tire 2 can maintain good wet performance from a new state until it needs to be replaced with the next tire 2. The tire 2 can suppress deterioration of wet performance due to wear and can achieve reduction in rolling resistance.

[0128] As described above, the tread ring 114 of the mold 104 for this tire 2 includes narrow groove ridges 144 that form the circumferential narrow grooves 18, and lateral blades 150 that form the lateral sipes 62. In the tire 2, the lateral sipes 62 are connected to the circumferential narrow grooves 18. The tread ring 114 has a ridge-blade connection portion. The ridge-blade connection portion is a connection portion between the narrow groove ridges 144 and the lateral blades 150.

[0129] As described above, the tread ring 114 has a plurality of circumferentially arranged segments 120. The narrow groove ridges 144 and the transverse blades 150 protrude inward from the reference plane BL of the pattern forming portion 136 of the tread ring 114. After the vulcanization process is completed, the mold 104 is opened to release the tire 2 from the mold 104. At this time, the segments 120 move radially outward as shown in Fig. 8, whereby the narrow groove ridges 144 and the lateral blades 150 are pulled out from the tread 4.

[0130] 8, the direction of the solid line LR represents the protruding direction of the narrow groove ridge 144 and the horizontal blade 150 at the end PE of the segment 120. The direction of the solid line LM represents the withdrawing direction of the narrow groove ridge 144 and the horizontal blade 150 at the end PE of the segment 120. The angle α is the angle between the solid lines LM and LR. The angle α represents the deviation of the withdrawing direction from the protruding direction at the end of the segment 120.

[0131] At the center PC of the segment 120, the pull-out direction of the narrow groove ridges 144 and the transverse blades 150 coincides with the protruding direction of the narrow groove ridges 144 and the transverse blades 150. However, the closer to the end PE of the segment 120, the more the pull-out direction deviates from the protruding direction, and the deviation of the pull-out direction from the protruding direction is greatest at the end PE of the segment 120. In other words, when the tire 2 is released from the mold 104, the closer to the end PE of the segment 120, the more the narrow groove ridges 144 and the transverse blades 150 are pulled out at an angle to their protruding direction. When the tire 2 is released from the mold 104, stress acting on the land portion 20 is concentrated near the connection portion of the protruding ridges and blades, and depending on the degree of this, there is a concern that tread chipping or blade damage may occur.

[0132] 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 is set as in a conventional mold, the angle α is 18.0 to 22.5 degrees. In contrast, in this mold 104, the number of segments 120 constituting the tread ring 114 is 17 or more. The angle α in this mold 104 is 10.6 degrees or less. By setting the number of segments 120 to 17 or more, this mold 104 can reduce the deviation of the drawing direction from the protruding direction of the narrow groove ridges 144 and the lateral blades. This mold 104 can reduce stress concentration that occurs near the connection portion of the ridge blades, which is caused by the deviation of the drawing direction from the protruding direction. 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 number of segments 120 constituting the tread ring 114 be 19 or more.

[0133] This mold 104 can suppress the occurrence of tread chipping and blade damage when releasing the tire 2 having the circumferential narrow grooves 18 and lateral sipes 62, which can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. This mold 104 can contribute to the stable production of high-quality and high-performance tires 2.

[0134] As described above, the number of segments 120 included in the tread ring 114 of this mold 104 is 17 or more. From the viewpoint of easy maintenance of the segments 120, the number of segments 120 is preferably 23 or less.

[0135] As described above, the plate-like portion 158 of the narrow groove ridge 144 extends straight. In the cross-sectional outline of the narrow groove ridge 144 shown in Figure 10, the plate-like portion 158 is represented by a straight line. The portion represented by this straight line is the first straight portion 160. In the cross-sectional outline of this narrow groove ridge 144, the portion that transitions from the plate-like portion 158 to the bulge portion 154 is an inner transition portion 162. The inner transition portion 162 is represented by a single arc having a radius R1. The position indicated by the symbol B1 is the boundary between the first straight portion 160 and the inner transition portion 162. The arc representing the inner transition portion 162 is tangent to the straight line representing the first straight portion 160 at the boundary B1.

[0136] As described above, the maximum width W2 of the bulge portion 154 is wider than the minimum width W1 of the plate-shaped portion 158. The radius R1 of the arc representing the inner transition portion 162 is larger than half the maximum width W2 of the bulge portion 154. This reduces the resistance when the narrow groove ridge 144 is pulled out of the tread 4. This prevents the rubber from getting caught at the ridge-blade connection portion. This mold 104 can reduce stress concentration that occurs near the connection portion. This mold 104 can prevent tread chipping and blade damage when the tire 2 is released. From this perspective, it is preferable that the maximum width W2 of the bulge portion 154 is wider than the minimum width W1 of the plate-shaped portion 158 and that the radius R1 of the arc representing the inner transition portion 162 is larger than half the maximum width W2 of the bulge portion 154.

[0137] The ratio W1 / W2 of the minimum width W1 of the plate-like portion 158 to the maximum width W2 of the bulging portion 154 is preferably 0.10 or more and 0.35 or less. By setting the ratio W1 / W2 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 mold 104 can reduce stress concentration that occurs near the connection portion. This mold 104 can prevent tread chipping and blade damage when the tire 2 is released. From this perspective, it is more preferable that the ratio W1 / W2 is 0.15 or greater. By setting the ratio W1 / W2 to 0.35 or less, the bulging portion 154 can form the widened portion 56 having the necessary groove volume. Even if the tread 4 wears and the lateral sipes 62 disappear, the exposed widened portion 56 can contribute to maintaining wet performance. From this perspective, it is more preferable that the ratio W1 / W2 be 0.30 or less.

[0138] The minimum width W1 of the plate-like portion 158 is preferably 2.5 mm or less. This allows the pair of wall surfaces 18S of the circumferential narrow groove 18 to effectively contact the narrow groove portion 60 formed by this plate-like portion 158 when the tread 4 comes into contact with the road surface and deforms. Deformation of the main land portion 28 is suppressed. This tire 2 can reduce rolling resistance. From this viewpoint, the minimum width W1 is 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 W1 is preferably 1.0 mm or more.

[0139] In the cross-sectional profile of the narrow groove ridge 144 shown in Figure 10, the portion where the plate-like portion 158 transitions to the tapered portion 156 is the outer transition portion 164. The outer transition portion 164 is represented by a single arc having a radius R2. The position indicated by the symbol B2 is the boundary between the first straight portion 160 and the outer transition portion 164. The arc representing the outer transition portion 164 meets the straight line representing the first straight portion 160 at the boundary B2. As described above, the contour of the wall surface of the funnel portion 58 of the tire 2 manufactured using this mold 104 is represented by a straight line. In the cross-sectional contour of the narrow groove ridge 144, the tapered portion 156 that forms this funnel portion 58 is represented by a straight line. The portion represented by this straight line is the second straight portion 166. The second straight portion 166 connects the edge corresponding position PE and the outer transition portion 164. The position indicated by symbol B3 is the boundary between the outer transition portion 164 and the second straight portion 166. The arc representing the outer transition portion 164 meets the straight line representing the second straight portion 166 at boundary B3.

[0140] The ratio R1 / R2 of the radius R1 of the arc representing the inner transition portion 162 to the radius R2 of the arc representing the outer transition portion 164 is preferably 1.5 or greater. This suppresses an increase in stress occurring in the inner transition portion 162 when the narrow groove ridge 144 and the lateral blade 150 are pulled out of the tread 4. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this perspective, the ratio R1 / R2 is more preferably 2.0 or greater. From the perspective that the bulge portion 154 can form the widened portion 56 having the required groove volume and that the widened portion 56 can effectively contribute to maintaining wet performance, the ratio R1 / R2 is preferably 20.0 or less.

[0141] As described above, the bulge 154 tapers from the maximum width point PXm toward the plate-shaped portion 158, and tapers from the maximum width point PXm toward the tip PHT. The portion of the bulge 154 including the tip PHT and the maximum width point PXm (hereinafter referred to as the rounded bottom portion 168) is represented by a single arc having a radius R3 in the cross-sectional outline of the narrow groove ridge 144 shown in Figure 10. The radius R3 of the arc representing the rounded bottom portion 168 is equal to half the length of the maximum width W2 of the bulge 154. 10 is the boundary between the inner transition portion 162 and the rounded bottom portion 168. The arc representing the rounded bottom portion 168 is in contact with the arc representing the inner transition portion 162 at the boundary B4.

[0142] The ratio R1 / R3 of the radius R1 of the arc defining the inner transition portion 162 to the radius R3 of the arc defining the rounded bottom portion 168 is preferably 3.0 or greater and 20.0 or less. Setting the ratio R1 / R3 to 3.0 or greater suppresses an increase in stress that occurs in the inner transition portion 162 when the narrow groove ridge 144 and the lateral blade 150 are pulled out of the tread 4. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this viewpoint, it is more preferable that the ratio R1 / R3 be 5.0 or greater. By setting the ratio R1 / R3 to 20.0 or less, the bulging portion 154 can form the widened portion 56 having the necessary groove volume, and the widened portion 56 can effectively contribute to maintaining wet performance. From this perspective, it is more preferable that the ratio R1 / R3 be 15.0 or less.

[0143] In Figure 10, the length indicated by the double arrow D1 is the protrusion length of the narrow groove ridge 144. The protrusion length D1 is represented by the distance from the reference plane BL to the tip PHT. The length indicated by the double arrow D2 is the protrusion length of the base 152 of the narrow groove ridge 144. The protrusion length D2 is represented by the distance from the reference plane BL to the boundary LPE between the base 152 and the bulge portion 154. The length indicated by the double arrow D3 is the protrusion length from the reference plane BL to the maximum width position PXm. The length indicated by the double arrow D4 is the protrusion length of the tapered portion 156. The protrusion length D4 is represented by the distance from the reference plane BL to the boundary LTP between the tapered portion 156 and the plate-like portion 158. The protrusion lengths D1, D2, D3, and D4 are measured along the width center line CH of the narrow groove ridge 144.

[0144] The ratio D2 / D1 of the protruding length D2 of the base portion 152 to the protruding length D1 of the narrow groove ridge 144 is preferably 0.25 or more and 0.70 or less. By setting the ratio D2 / D1 to 0.25 or greater, the body portion 54 is formed by the base portion 152 to have the necessary groove depth. 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 60. The tire 2 manufactured using this mold 104 can reduce rolling resistance. From this perspective, 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 from the tread 4 is reduced. The rubber is prevented from getting caught at the ridge-blade connection portion. This mold 104 can reduce stress concentration that occurs near the connection portion. This mold 104 can prevent tread chipping and blade damage from occurring when the tire 2 is released. From this perspective, it is more preferable that the ratio D2 / D1 is 0.65 or less.

[0145] The ratio D4 / D1 of the protruding length D4 of the tapered portion 156 to the protruding length D1 of the narrow groove ridge 144 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 58 formed by the tapered portion 156 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 main land portion 28. The tire 2 manufactured using this mold 104 has good durability. By setting the ratio D4 / D1 to 0.14 or less, the narrow groove portion 60 having the required length is formed. 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 60. The tire 2 manufactured using this mold 104 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 and blade damage, 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.

[0146] Fig. 12 is a cross-sectional view showing a part of Fig. 7. Fig. 12 shows how the narrow groove ridges 144 and the lateral blades 150 of the mold 104 form the circumferential narrow grooves 18 and the lateral sipes 62 of the tire 2. The length indicated by the double-headed arrow D5 in Fig. 12 is the protruding length of the lateral blades 150. The protruding length D5 is expressed as the shortest distance from the reference plane BL of the pattern forming portion 136 to the tip PBT of the lateral blades 150.

[0147] The protruding length D5 of the lateral blade 150 is longer than the protruding length D2 of the base 152. This allows the lateral sipe 62 formed by the lateral blade 150 to function as an edge component from the initial to intermediate stages of wear. A tire 2 manufactured with this mold 104 can maintain good wet performance. The protruding length D5 of the lateral blade 150 is shorter than the protruding length D3 from the reference plane BL to the maximum width position PXm of the bulging portion 154 of the narrow groove ridge 144. This reduces the impact of the lateral sipe 62 on the rigidity of the tread 4. The body portion 54 of the circumferential narrow groove 18 (specifically, the narrow groove portion 60) can effectively contribute to suppressing deformation of the main land portion 28. 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. This mold 104 can reduce stress concentration occurring near the connection portion. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. This mold 104 can suppress the occurrence of tread chipping and blade damage when releasing a tire 2 having circumferential narrow grooves 18 and lateral sipes 62 that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. From this perspective, it is preferable that the protruding length D2 of the base 152, the protruding length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulging portion 154, and the protruding length D5 of the lateral blade 150 satisfy the following formula: Formula: D2≦D5≦D3

[0148] When the protrusion length D2 of the base 152, the protrusion length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulge portion 154, and the protrusion length D5 of the horizontal blade 150 satisfy the above formula, the occurrence of tread chipping and blade damage when releasing the tire 2 from the mold 104 is suppressed, and further, from the viewpoint that the tire 2 manufactured using this mold 104 can suppress deterioration of wet performance due to wear and achieve reduced rolling resistance, it is even more preferable that the ratio D2 / D5 of the protrusion length D2 to the protrusion length D5 is 0.40 or more and 0.90 or less, and the ratio D3 / D5 of the protrusion length D3 to the protrusion length D5 is 1.05 or more and 2.00 or less.

[0149] 9, the solid line YL represents the length direction of the horizontal blade 150. The angle β represents the angle between the length direction of the horizontal blade 150 and the axial direction. In the present invention, this angle β is the angle between the horizontal blade 150 and the axial direction.

[0150] The angle β is expressed in the range of -90 degrees to 90 degrees. When the angle β is 0 degrees, the longitudinal direction of the lateral blade 150 coincides with the axial direction. When the angle β is expressed as a negative number, the orientation of the longitudinal direction of the lateral blade 150 relative to the axial direction is opposite to the orientation of the longitudinal direction of the lateral blade 150 relative to the axial direction when the angle β is expressed as a positive number.

[0151] In this mold 104, the angle β 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 ridge-blade connection portion is suppressed when the narrow groove ridge 144 and the transverse blade 150 are pulled out of the tread 4. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this viewpoint, the angle β is more preferably equal to or greater than -25 degrees and equal to or less than 25 degrees.

[0152] As described above, the lateral blade 150 extends in a zigzag pattern in its length direction and protruding direction. This allows a pair of wall surfaces 62W of the lateral sipe 62 formed by this lateral blade 150 to mesh effectively with each other. This suppresses deformation of the main land portion 28. This tire 2 can reduce rolling resistance. From this perspective, it is preferable that the lateral blade 150 extends in a zigzag pattern in its length direction and protruding direction.

[0153] The length indicated by the double arrow TB in FIG. The thickness TB of the lateral blade 150 is preferably 0.4 mm or more from the viewpoint of suppressing the occurrence of breakage or bending of the lateral blade 150. The thickness TB of the lateral blade 150 is preferably 0.7 mm or less from the viewpoint of allowing the lateral sipes 62 formed by this lateral blade 150 to effectively contribute to suppressing deformation of the main land portion 28.

[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. 13 , 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 surface 124, the lateral blade 150 is composed of two small blade pieces. In this case, the rigidity of the entire lateral blade 150 decreases. Even if the number of segments 120 included in the tread ring 114 is set to 17 or more and the mold 104 is configured so that an unusual force is unlikely to act on the lateral blade 150 when the tire 2 is released from the mold 104, damage such as breakage or bending of the lateral blade 150 may occur. 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 horizontal blade 150 closest to the dividing surface 124 to the dividing surface 124. This shortest circumferential distance Lm can be obtained by measuring the circumferential distance from the tip PBT of the horizontal blade 150 to the dividing surface 124.

[0160] The radius R1 of the arc representing the inward transition portion 162 of the narrow groove ridge 144 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. This prevents the rubber from getting caught at the ridge-blade connection portion. This mold 104 can reduce stress concentration that occurs near the connection portion. This mold 104 can prevent tread chipping and blade damage when the tire 2 is released. From this perspective, it is preferable that the radius R1 of the arc representing the inward transition portion 162 be larger than the shortest circumferential distance Lm. Specifically, the ratio R1 / Lm of the radius R1 of the arc representing the inward transition portion 162 to the shortest circumferential distance Lm is preferably 1.1 or greater, and more preferably 1.5 or greater. From the viewpoint that the bulge portion 154 can form the widened portion 56 having the necessary groove volume and that the widened portion 56 can effectively contribute to maintaining wet performance, it is preferable that the ratio R1 / Lm be 8.0 or less, and more preferably 7.0 or less.

[0161] 14 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. 14 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 of the narrow groove ridge 144 and the lateral blade 150 in the pulling direction relative to the protruding direction is greatest at the end PE 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] 15 shows how the tire 2 is formed by replacing the lateral blade 150 of the mold 104 with a modified lateral blade 180. The lateral blade 180 forms the lateral sipe 62.

[0165] The horizontal blade 180 is located between the two narrow groove ridges 144, similar to the horizontal blade 150. The horizontal blade 180 bridges between the two narrow groove ridges 144. The horizontal blade 180 has a central portion 182 and a pair of end portions 184. The central portion 182 is located in the center of the horizontal blade 180 in the longitudinal direction. The pair of end portions 184 are each located outside the central portion 182 in the longitudinal direction of the horizontal blade 180. The end portions 184 are located between the central portion 182 and the narrow groove ridges 144. The horizontal blade 180 connects to the narrow groove ridges 144 at the end portions 184.

[0166] Although not shown, the lateral blade 180 extends straight in its length direction and protruding direction. The lateral blade 180 is a two-dimensional blade. The lateral blade 180 may be configured to extend in a zigzag pattern in its length direction and protruding direction. In other words, the lateral blade 180 may be a three-dimensional blade.

[0167] The protruding length of the end 184 is expressed as the length from the reference surface BL of the pattern forming portion 136 to the bottom 184T of the end 184, measured along the normal to the reference surface BL. 15, the position indicated by the symbol PCN is the connecting portion between the narrow groove ridge 144 and the horizontal blade 180, i.e., the radially inner end of the ridge-blade connecting portion. The radially inner end PCN is included in the bottom 184T of the end portion 184. The radially inner end PCN is the end of the bottom 184T of the end portion 184 on the narrow groove ridge 144 side.

[0168] The length indicated by the double-headed arrow D6 is the distance from the reference plane BL of the pattern forming portion 136 to the radially inner end PCN of the ridge-blade connection portion. The protrusion length D6 is the protrusion length of the end 184 at the ridge-blade connection portion. In the present invention, the protrusion length of the end 184 of the horizontal blade 180 is expressed as the protrusion length D6 of the end 184 at the ridge-blade connection portion.

[0169] 15, the end portion 184 has a uniform protrusion length D6 in its length direction. The end portion 184 may be configured such that the protrusion length of the end portion 184 gradually increases from the ridge blade connection portion toward the central portion 182.

[0170] The protruding length of the central portion 182 is expressed as the length from the reference surface BL of the pattern forming portion 136 to the bottom 182T of the central portion 182, measured along the normal to the reference surface BL.

[0171] The length indicated by the double-headed arrow D7 is the protruding length of the central portion 182 of the horizontal blade 180. In the present invention, the protruding length D7 of the central portion 182 is expressed as the longest distance from the reference plane BL of the pattern forming portion 136 to the tip 182T of the central portion 182. The protruding length D7 is also called the longest protruding length.

[0172] 15, central portion 182 has a uniform protrusion length D7 in the length direction. Central portion 182 may be configured such that the protrusion length of central portion 182 gradually decreases from the position exhibiting the longest protrusion length D7 toward end portion 184.

[0173] As shown in FIG. 15, the protruding length D6 of the lateral blade 180 at the end 184 of the lateral blade 180 is shorter than the protruding length D7 of the lateral blade 180 at the central portion 182 of the lateral blade 180. As a result, even if the tip 182T of the central portion 182 of the horizontal blade 180 is positioned near the maximum width position PXm of the bulging portion 154 of the narrow groove ridge 144, the protruding length D6 of the end 184 connected to the narrow groove ridge 144 is short, so that when the narrow groove ridge 144 and the horizontal blade 180 are pulled out of the tread 4, the rubber is prevented from getting caught at the ridge-blade connection portion. This mold 104 can reduce stress concentration that occurs near the connection portion. Even if the tip 182T of the central portion 182 of the horizontal blade 180 is positioned near the maximum width position PXm of the bulging portion 154 of the narrow groove ridge 144, this mold 104 can prevent tread chipping and blade damage when the tire 2 is released. This mold 104 positions the tip 182T of the central portion 182 of the lateral blade 180 near the maximum width position PXm of the bulging portion 154 of the narrow groove ridge 144, thereby making it possible to provide the tire 2 with a lateral sipe 62 that can function as an edge component until the final stage of wear when the tire 2 needs to be replaced. In this case, the tire 2 can maintain good wet performance from a new state until the tire 2 needs to be replaced. From this perspective, it is preferable that the protrusion length D6 of the lateral blade 180 at the end 184 of the lateral blade 180 be shorter than the protrusion length D7 of the lateral blade 180 at the central portion 182 of the lateral blade 180.

[0174] The protruding length D6 of the end 184 of the lateral blade 180 is longer than the protruding length D2 of the base 152. This allows the end of the lateral sipe 62 formed by the end 184 of the lateral blade 150 to function as an edge component from the initial to intermediate stages of wear. The tire 2 manufactured using this mold 104 can maintain good wet performance. The protruding length D6 of the end 184 is shorter than the protruding length D3 from the reference plane BL to the maximum width position PXm of the bulging portion 154 of the narrow groove ridge 144. This suppresses the impact of the end of the lateral sipe 62 on the rigidity of the tread 4. The body portion 54 of the circumferential narrow groove 18 (specifically, the narrow groove portion 60) can effectively contribute to suppressing deformation of the main land portion 28. 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 180 are pulled out of the tread 4, catching of rubber at the ridge-blade connecting portion is suppressed. This mold 104 can reduce stress concentration occurring near the connecting portion. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. This mold 104 can suppress the occurrence of tread chipping and blade damage when releasing a tire 2 having circumferential narrow grooves 18 and lateral sipes 62 that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. From this perspective, it is preferable that the protrusion length D2 of the base 152, the protrusion length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulging portion 154, and the protrusion length D6 of the lateral blade 180 at the end 184 of the lateral blade 180 satisfy the following formula: Formula: D2≦D6≦D3

[0175] When the protrusion length D2 of the base 152, the protrusion length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulge portion 154, and the protrusion length D6 of the end 184 of the horizontal blade 180 satisfy the above formula, the occurrence of tread chipping and blade damage when releasing the tire 2 from the mold 104 is suppressed, and further, from the viewpoint that the tire 2 manufactured using this mold 104 can suppress deterioration of wet performance due to wear and achieve reduced rolling resistance, it is even more preferable that the ratio D2 / D6 of the protrusion length D2 to the protrusion length D6 is 0.40 or more and 0.90 or less, and the ratio D3 / D5 of the protrusion length D3 to the protrusion length D6 is 1.05 or more and 2.00 or less.

[0176] As described above, the protruding length D6 of the horizontal blade 180 at the end 184 of the horizontal blade 180 is shorter than the protruding length D7 of the horizontal blade 180 at the central portion 182 of the horizontal blade 180. Specifically, the difference (D7 - D6) between the protruding length D7 of the central portion 182 of the horizontal blade 180 and the protruding length D6 of the end 184 of the horizontal blade 180 is preferably 2.0 mm or more and 8.5 mm or less. By setting the difference (D7-D6) to 2.0 mm or more, the lateral sipes 62 formed only by the central portion 182, which are exposed after the lateral sipes 62 formed by the central portion 182 and the end portions 184 disappear, can function as edge components until the final stage of wear when the tire 2 needs to be replaced. This tire 2 can maintain good wet performance from a new state until the tire 2 needs to be replaced. From this perspective, it is more preferable that the difference (D7-D6) be 3.0 mm or more. Setting the difference (D7-D6) to 8.5 mm or less reduces the stress acting on the lateral blade 180 when the narrow groove ridge 144 and the lateral blade 180 are pulled out of the tread 4. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this perspective, it is more preferable that the difference (D7-D6) be 7.5 mm or less.

[0177] 15, the protruding length D7 of the central portion of the horizontal blade 180 is shorter than the protruding length D1 of the narrow groove ridges. Specifically, the difference (D1-D7) between the protruding length D1 of the narrow groove ridges and the protruding length D7 of the central portion of the horizontal blade 180 is preferably 1.0 mm or more and 6.5 mm or less. By setting the difference (D1-D7) to 1.0 mm or more, the stress acting on the lateral blade 180 is reduced when the narrow groove ridge 144 and the lateral blade 180 are pulled out of the tread 4. This mold 104 can suppress the occurrence of tread chipping and blade damage when the tire 2 is released. From this viewpoint, it is more preferable that the difference (D1-D7) be 2.0 mm or more. By setting the difference (D1-D7) to 6.5 mm or less, the lateral sipes 62 can function as edge components until the final stage of wear when replacement of the tire 2 is required. The tire 2 can maintain good wet performance from a new state until replacement of the tire 2 is required. From this viewpoint, it is more preferable that the difference (D1-D7) be 5.5 mm or less.

[0178] As shown in FIG. 15 , the protrusion length D7 of the central portion 182 of the lateral blade 180 is longer than the protrusion length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulging portion 154. As described above, the protrusion length D7 of the central portion of the lateral blade 180 is shorter than the protrusion length D1 of the narrow groove ridge. This allows the lateral sipe 62 to effectively function as an edge component after the bulging portion 154 has disappeared to the position PXm indicating the maximum width W1, until the final stage of wear when the tire 2 needs to be replaced. This tire 2 can maintain good wet performance from a new state until the tire 2 needs to be replaced. From this perspective, it is preferable that the protrusion length D7 of the central portion 182 of the lateral blade 180 be longer than the protrusion length D3 from the reference plane BL to the position PXm indicating the maximum width W2 of the bulging portion 154, but shorter than the protrusion length D1 of the narrow groove ridge. In other words, the tip 182T of the central portion 182 is preferably located between the position PXm indicating the maximum width W2 of the bulging portion 154 and the tip PHT of the narrow groove ridge 144 in the radial direction.

[0179] The length indicated by the double-headed arrow W3 in Figure 15 is the axial width of the horizontal blade 180. The distance between one narrow groove ridge 144 and the other narrow groove ridge 144 is greatest between the plate-shaped portion 158 of one narrow groove ridge 144 and the plate-shaped portion 158 of the other narrow groove ridge 144. The axial direction W3 of the horizontal blade bridging the two narrow groove ridges 144 is represented by the axial distance between one plate-shaped portion 158 and the other plate-shaped portion 158. The length indicated by the double-headed arrow W4 is the axial width of the central portion 182 of the cross blade 180. The axial width W4 of the central portion 182 is expressed as the axial distance from the end of the central portion 182 on one narrow groove ridge 144 side to the end of the central portion 182 on the other narrow groove ridge 144 side.

[0180] The ratio W4 / W3 of the axial width W4 of the central portion 182 to the width W3 of the lateral blade 180 is preferably 0.4 or more and 0.7 or less. By setting the ratio W4 / W3 to 0.4 or greater, the lateral sipes 62 formed only by the central portion 182, which are exposed after the lateral sipes 62 formed by the central portion 182 and the end portions 184 disappear, can function as edge components until the final stage of wear when replacement of the tire 2 is required. This tire 2 can maintain good wet performance from a new state until replacement of the tire 2 is required. From this viewpoint, it is more preferable that the ratio W4 / W3 be 0.5 or greater. By setting the ratio W4 / W3 to 0.7 or less, it is possible to prevent the rubber from getting caught at the ridge-blade connection portion when the narrow groove ridge 144 and the transverse blade 180 are pulled out of the tread 4. This mold 104 can reduce stress concentration that occurs near the connection portion. This mold 104 can also prevent tread chipping and blade damage when the tire 2 is released. From this perspective, it is more preferable that the ratio W4 / W3 be 0.6 or less.

[0181] As shown in Fig. 15, the boundary between the end portion 184 and the central portion 182 is rounded. In Fig. 15, arrow R4 indicates the radius of the rounded boundary. Rounding the boundary between the end portion 184 and the central portion 182 reduces the concentration of strain at the boundary. When the lateral blade 180 is pulled out of the tread 4, the rubber is prevented from getting caught at the boundary portion, thereby reducing the resistance force when the lateral blade 180 is pulled out of the tread 4. This mold 104 can reduce stress concentration that occurs near the ridge blade connection portion. 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 boundary between the end portion 184 and the central portion 182 be rounded. In this case, the radius R4 of the rounding of the boundary is preferably 0.5 mm or more and 5.0 mm or less.

[0182] As shown in Fig. 15, the central portion 182 has corners that are rounded. In Fig. 15, arrow R5 indicates the radius of the rounded corners. Rounding the corners of the central portion 182 reduces the concentration of strain at the corners. When the lateral blade 180 is pulled out of the tread 4, the rubber is prevented from getting caught on the corners, thereby reducing the resistance force when the lateral blade 180 is pulled out of the tread 4. This mold 104 can reduce stress concentration that occurs near the ridge blade connection portion. This mold 104 can prevent tread chipping and blade damage when the tire 2 is released. From this perspective, it is preferable that the corners of the central portion 182 are rounded. In this case, the radius R5 of the rounded corners is preferably 0.5 mm or more and 5.0 mm or less.

[0183] As is clear from the above explanation, according to the present invention, it is possible to obtain a tire mold and a method for manufacturing a heavy-duty tire that can contribute to the stable manufacture of a tire 2 having circumferential narrow grooves 18 and lateral sipes 62 that can suppress the occurrence of tread chipping and blade damage when releasing the tire 2 and can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear. [Industrial Applicability]

[0184] The technology described above, which can contribute to the stable production of tires having circumferential narrow grooves and lateral sipes that can suppress the occurrence of tread chipping and blade damage when releasing a tire and that can contribute to reducing rolling resistance and suppressing deterioration of wet performance due to wear, can be applied to various tire molds and tire manufacturing methods.

[0185] [Note] The present invention includes the following aspects.

[0186] [1] A mold for forming a heavy-duty tire, comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves, the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion, the body portion including a narrow groove portion connected to the widened portion, and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion, 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 narrow groove protrusion that protrudes from its reference surface and forms the circumferential narrow groove, and a lateral blade that protrudes from the reference surface and forms the lateral sipe, The narrow groove ridge includes a base portion that forms the body portion and a bulge portion that forms the widened portion, the base portion includes a plate-like portion that forms the narrow groove portion, The tread ring has a plurality of dividing surfaces that cross the pattern forming portion, A plurality of dividing surfaces divide the tread ring into a plurality of segments arranged in a circumferential direction, The number of the segments included in the tread ring is 17 or more. Tire mold. [2] In the cross-sectional contour of the narrow groove ridge along a plane perpendicular to the longitudinal direction of the narrow groove ridge, the portion transitioning from the plate-like portion to the bulge portion is an inner transition portion, and the inner transition portion is represented by an arc having a radius R1; The minimum width W1 of the plate-like portion is narrower than the maximum width W2 of the bulge portion, The tire mold according to [1] above, wherein the radius R1 of the arc representing the inner transition portion is greater than half the maximum width W2 of the bulge portion. [3] The body portion of the circumferential narrow groove has a funnel portion located radially outward of the narrow groove portion, the base includes a tapered portion that forms the funnel; In the cross-sectional profile of the narrow groove ridge, a portion transitioning from the plate-like portion to the tapered portion is an outer transition portion, and the outer transition portion is represented by an arc having a radius R2, The tire mold described in [2] above, wherein the ratio R1 / R2 of the radius R1 of the arc representing the inner transition portion to the radius R2 of the arc representing the outer transition portion is 1.5 or greater. [4] The tire mold according to the above-mentioned [2] or [3], wherein the shortest distance from the lateral blade closest to the dividing surface to the dividing surface is smaller than the radius R1 of the arc representing the inner transition portion. [5] A tire mold according to any one of the above [1] to [4], wherein the ratio W1 / W2 of the minimum width W1 of the plate-like portion to the maximum width W2 of the bulge portion is 0.10 or more and 0.35 or less. [6] The tire mold according to any one of [1] to [5] above, wherein the minimum width W1 of the plate-shaped portion is 2.5 mm or less. [7] The tire mold according to any one of the above [1] to [6], wherein the ratio D2 / D1 of the protruding length D2 of the base to the protruding length D1 of the narrow groove ridge is 0.25 or more and 0.70 or less. [8] A tire mold according to any one of the above [1] to [7], wherein the protruding length D2 of the base, the protruding length D3 from the reference plane to a position indicating the maximum width W2 of the bulge portion, and the protruding length D5 of the lateral blade satisfy the following formula: Formula: D2≦D5≦D3 [9] The tire mold according to any one of [1] to [8] above, wherein the angle formed by the horizontal blade with respect to the axial direction is between -35 degrees and 35 degrees.

[10] The tire mold according to any one of [1] to [9] above, wherein the horizontal blades extend in a zigzag pattern in the protruding direction and in the longitudinal direction.

[11] The tire mold according to any one of [1] to

[10] above, wherein the thickness of the lateral blade is 0.4 mm or more and 0.7 mm or less.

[12] The tire mold according to any one of [1] to

[11] above, wherein in a development view of the pattern forming portion, the contour of the dividing surface includes at least one arc.

[13] A tire mold according to any one of [1] to

[12] above, wherein the protruding length D6 of the lateral blade at the end of the lateral blade is shorter than the protruding length D7 of the lateral blade at the center of the lateral blade.

[14] The tire mold described in

[13] above, wherein the protruding length D2 of the base, the protruding length D3 from the reference plane to a position indicating the maximum width W2 of the bulge portion, and the protruding length D6 of the lateral blade at the end of the lateral blade satisfy the following formula: Formula: D2≦D6≦D3

[15] A method for manufacturing a heavy-duty tire comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves; the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion; the body portion including a narrow groove portion connected to the widened portion; and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion, pressurizing and heating a green tire for said tire in a mold; A method for manufacturing a heavy-duty tire, wherein the mold is the tire mold according to any one of [1] to

[14] above. [Explanation of symbols]

[0187] 2. Tires 4. Tread 6. Tread surface 18... Circumferential narrow groove 54 Torso 56 Widened section 58...Funnel part 60...Narrow groove part 62 Horizontal sipes 104···Mold 114 Tread ring 120 segments 124, 124m...Divided surface 136 Pattern forming section 144...Narrow groove convex strip 150, 180... Horizontal blade 152...Base 154...bulge 156 Tapered section 158 Plate-shaped part 162 Inner transition section 164...outer transition part 178, 178b, 178n pitch patterns 182...Central part 184...End

Claims

1. A mold for forming a heavy-duty tire, comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves, the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion, the body portion including a narrow groove portion connected to the widened portion, and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion, 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 narrow groove protrusion that protrudes from its reference surface and forms the circumferential narrow groove, and a lateral blade that protrudes from the reference surface and forms the lateral sipe, The narrow groove ridge includes a base portion that forms the body portion and a bulge portion that forms the widened portion, the base portion includes a plate-like portion that forms the narrow groove portion, The tread ring has a plurality of dividing surfaces that cross the pattern forming portion, A plurality of dividing surfaces divide the tread ring into a plurality of segments arranged in a circumferential direction, The number of the segments included in the tread ring is 17 or more. Tire mold.

2. In a cross-sectional outline of the narrow groove ridge along a plane perpendicular to the longitudinal direction of the narrow groove ridge, a portion transitioning from the plate-like portion to the bulge portion is an inner transition portion, and the inner transition portion is represented by an arc having a radius R1, The minimum width W1 of the plate-like portion is narrower than the maximum width W2 of the bulging portion, The radius R1 of the arc representing the inner transition portion is greater than half the maximum width W2 of the bulge portion. The tire mold of claim 1 .

3. a ratio W1 / W2 of a minimum width W1 of the plate-like portion to a maximum width W2 of the bulging portion is 0.10 or more and 0.35 or less; The tire mold of claim 1 .

4. The minimum width W1 of the plate-shaped portion is 2.5 mm or less. The tire mold of claim 1 .

5. a body portion of the circumferential narrow groove having a funnel portion located radially outward of the narrow groove portion, the base includes a tapered portion that forms the funnel; In the cross-sectional contour of the narrow groove ridge, a portion transitioning from the plate-like portion to the tapered portion is an outer transition portion, and the outer transition portion is represented by an arc having a radius R2, a ratio R1 / R2 of the radius R1 of the arc representing the inner transition portion to the radius R2 of the arc representing the outer transition portion is 1.5 or more; The tire mold of claim 2.

6. a ratio D2 / D1 of a protruding length D2 of the base portion to a protruding length D1 of the narrow groove convex streak is 0.25 or more and 0.70 or less; The tire mold of claim 1 .

7. The protruding length D2 of the base portion, the protruding length D3 from the reference plane to a position indicating the maximum width W2 of the bulging portion, and the protruding length D5 of the horizontal blade satisfy the following formula: The tire mold of claim 1 . Formula: D2≦D5≦D3

8. The angle formed by the horizontal blade with respect to the axial direction is equal to or greater than -35 degrees and equal to or less than 35 degrees. The tire mold of claim 1 .

9. The horizontal blades extend in a zigzag pattern in their protruding and length directions. The tire mold of claim 1 .

10. The thickness of the horizontal blade is 0.4 mm or more and 0.7 mm or less. The tire mold of claim 1 .

11. The shortest distance from the horizontal blade closest to the dividing surface to the dividing surface is shorter than the radius R1 of the arc representing the inner transition portion. The tire mold of claim 2.

12. In a development view of the pattern forming portion, the outline of the dividing surface includes at least one arc. The tire mold of claim 1 .

13. A protruding length D6 of the horizontal blade at the end portion of the horizontal blade is shorter than a protruding length D7 of the horizontal blade at the central portion of the horizontal blade. The tire mold of claim 1 .

14. The protruding length D2 of the base portion, the protruding length D3 from the reference plane to a position indicating the maximum width W2 of the bulging portion, and the protruding length D6 of the horizontal blade at the end of the horizontal blade satisfy the following formula: The tire mold of claim 13. Formula: D2≦D6≦D3

15. A method for manufacturing a heavy-duty tire comprising: a tread having a tread pattern, the tread pattern including circumferential narrow grooves and lateral sipes connected to the circumferential narrow grooves; the circumferential narrow grooves including a body portion and a widened portion located radially inward of the body portion; the body portion including a narrow groove portion connected to the widened portion; and when the tread comes into contact with a road surface and deforms, a pair of wall surfaces of the circumferential narrow grooves come into contact with each other at the narrow groove portion, pressurizing and heating a green tire for said tire in a mold; The mold is a tire mold according to any one of claims 1 to 14. A method for manufacturing heavy-duty tires.

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